diff --git a/api/src/config/index.ts b/api/src/config/index.ts
index 9a9936b6..abba4b5a 100644
--- a/api/src/config/index.ts
+++ b/api/src/config/index.ts
@@ -73,7 +73,7 @@ export const config: Config = {
     grant3rdPartyCookie: true,
     onlyAllowOrigins: process.env.FRONTEND_ORIGIN
       ? process.env.FRONTEND_ORIGIN.split(',').map((origin) => origin.trim())
-      : [undefined], // ['http://example.com', 'https://example.com'],
+      : [], // ['http://example.com', 'https://example.com'],
   },
   session: {
     secret: process.env.SESSION_SECRET || 'changeme',
@@ -91,7 +91,9 @@ export const config: Config = {
   emails: {
     isEnabled: process.env.EMAIL_SMTP_ENABLED === 'true' || false,
     smtp: {
-      port: parseInt(process.env.EMAIL_SMTP_PORT) || 25,
+      port: process.env.EMAIL_SMTP_PORT
+        ? parseInt(process.env.EMAIL_SMTP_PORT)
+        : 25,
       host: process.env.EMAIL_SMTP_HOST || 'localhost',
       ignoreTLS: false,
       secure: process.env.EMAIL_SMTP_SECURE === 'true' || false,
diff --git a/api/src/i18n/controllers/language.controller.spec.ts b/api/src/i18n/controllers/language.controller.spec.ts
index dcaa9a7f..d260a502 100644
--- a/api/src/i18n/controllers/language.controller.spec.ts
+++ b/api/src/i18n/controllers/language.controller.spec.ts
@@ -69,7 +69,7 @@ describe('LanguageController', () => {
     }).compile();
     languageService = module.get<LanguageService>(LanguageService);
     languageController = module.get<LanguageController>(LanguageController);
-    language = await languageService.findOne({ code: 'en' });
+    language = (await languageService.findOne({ code: 'en' })) as Language;
   });
 
   afterEach(jest.clearAllMocks);
@@ -92,7 +92,7 @@ describe('LanguageController', () => {
 
       expect(languageService.findOne).toHaveBeenCalledWith(language.id);
       expect(result).toEqualPayload(
-        languageFixtures.find(({ code }) => code === language.code),
+        languageFixtures.find(({ code }) => code === language.code) as Language,
       );
     });
   });
@@ -142,7 +142,9 @@ describe('LanguageController', () => {
     it('should mark a language as default', async () => {
       jest.spyOn(languageService, 'updateOne');
       const translationUpdateDto = { isDefault: true };
-      const frLang = await languageService.findOne({ code: 'fr' });
+      const frLang = (await languageService.findOne({
+        code: 'fr',
+      })) as Language;
       const result = await languageController.updateOne(
         frLang.id,
         translationUpdateDto,
@@ -157,7 +159,9 @@ describe('LanguageController', () => {
         ...translationUpdateDto,
       });
 
-      const enLang = await languageService.findOne({ code: 'en' });
+      const enLang = (await languageService.findOne({
+        code: 'en',
+      })) as Language;
       expect(enLang.isDefault).toBe(false);
     });
 
@@ -171,7 +175,9 @@ describe('LanguageController', () => {
 
   describe('deleteOne', () => {
     it('should throw when attempting to delete the default language', async () => {
-      const defaultLang = await languageService.findOne({ isDefault: true });
+      const defaultLang = (await languageService.findOne({
+        isDefault: true,
+      })) as Language;
 
       await expect(
         languageController.deleteOne(defaultLang.id),
diff --git a/api/src/i18n/controllers/translation.controller.spec.ts b/api/src/i18n/controllers/translation.controller.spec.ts
index 87e56d6f..484c90a2 100644
--- a/api/src/i18n/controllers/translation.controller.spec.ts
+++ b/api/src/i18n/controllers/translation.controller.spec.ts
@@ -141,7 +141,9 @@ describe('TranslationController', () => {
     translationController = module.get<TranslationController>(
       TranslationController,
     );
-    translation = await translationService.findOne({ str: 'Welcome' });
+    translation = (await translationService.findOne({
+      str: 'Welcome',
+    })) as Translation;
   });
 
   afterEach(jest.clearAllMocks);
@@ -164,7 +166,9 @@ describe('TranslationController', () => {
 
       expect(translationService.findOne).toHaveBeenCalledWith(translation.id);
       expect(result).toEqualPayload(
-        translationFixtures.find(({ str }) => str === translation.str),
+        translationFixtures.find(
+          ({ str }) => str === translation.str,
+        ) as Translation,
       );
     });
   });
diff --git a/api/src/i18n/i18n.module.ts b/api/src/i18n/i18n.module.ts
index 8ad4238f..e8b15e1e 100644
--- a/api/src/i18n/i18n.module.ts
+++ b/api/src/i18n/i18n.module.ts
@@ -11,6 +11,7 @@ import {
   forwardRef,
   Global,
   Inject,
+  InternalServerErrorException,
   Module,
 } from '@nestjs/common';
 import { HttpAdapterHost } from '@nestjs/core';
@@ -54,6 +55,11 @@ export class I18nModule extends NativeI18nModule {
 
   static forRoot(options: I18nOptions): DynamicModule {
     const { imports, providers, controllers, exports } = super.forRoot(options);
+    if (!providers || !exports) {
+      throw new InternalServerErrorException(
+        'I18n: Unable to find providers and/or exports forRoot()',
+      );
+    }
     return {
       module: I18nModule,
       imports: (imports || []).concat([
diff --git a/api/src/i18n/services/i18n.service.ts b/api/src/i18n/services/i18n.service.ts
index 9e5b93aa..39fd0fd0 100644
--- a/api/src/i18n/services/i18n.service.ts
+++ b/api/src/i18n/services/i18n.service.ts
@@ -6,7 +6,7 @@
  * 2. All derivative works must include clear attribution to the original creator and software, Hexastack and Hexabot, in a prominent location (e.g., in the software's "About" section, documentation, and README file).
  */
 
-import { Injectable } from '@nestjs/common';
+import { Injectable, InternalServerErrorException } from '@nestjs/common';
 import {
   I18nService as NativeI18nService,
   Path,
@@ -34,6 +34,11 @@ export class I18nService<
       ...options,
     };
     let { lang } = options;
+
+    if (!lang) {
+      throw new InternalServerErrorException('I18nService: lang is undefined');
+    }
+
     lang = this.resolveLanguage(lang);
 
     // Translate block message, button text, ...
diff --git a/api/src/i18n/services/language.service.ts b/api/src/i18n/services/language.service.ts
index 4b532101..7fbeeb70 100644
--- a/api/src/i18n/services/language.service.ts
+++ b/api/src/i18n/services/language.service.ts
@@ -7,7 +7,11 @@
  */
 
 import { CACHE_MANAGER } from '@nestjs/cache-manager';
-import { Inject, Injectable } from '@nestjs/common';
+import {
+  Inject,
+  Injectable,
+  InternalServerErrorException,
+} from '@nestjs/common';
 import { Cache } from 'cache-manager';
 
 import {
@@ -53,7 +57,13 @@ export class LanguageService extends BaseService<Language> {
    */
   @Cacheable(DEFAULT_LANGUAGE_CACHE_KEY)
   async getDefaultLanguage() {
-    return await this.findOne({ isDefault: true });
+    const defaultLanguage = await this.findOne({ isDefault: true });
+    if (!defaultLanguage) {
+      throw new InternalServerErrorException(
+        'Default language not found: getDefaultLanguage()',
+      );
+    }
+    return defaultLanguage;
   }
 
   /**
diff --git a/api/src/i18n/services/translation.service.ts b/api/src/i18n/services/translation.service.ts
index a5770794..117411c6 100644
--- a/api/src/i18n/services/translation.service.ts
+++ b/api/src/i18n/services/translation.service.ts
@@ -100,6 +100,7 @@ export class TranslationService extends BaseService<Translation> {
     }
     // Add fallback messages
     if (
+      block.options &&
       'fallback' in block.options &&
       block.options.fallback &&
       'message' in block.options.fallback &&
diff --git a/api/src/user/controllers/auth.controller.spec.ts b/api/src/user/controllers/auth.controller.spec.ts
index 706de31f..5b3ca462 100644
--- a/api/src/user/controllers/auth.controller.spec.ts
+++ b/api/src/user/controllers/auth.controller.spec.ts
@@ -28,6 +28,7 @@ import { I18nService } from '@/i18n/services/i18n.service';
 import { LanguageService } from '@/i18n/services/language.service';
 import { LoggerService } from '@/logger/logger.service';
 import { getRandom } from '@/utils/helpers/safeRandom';
+import { installLanguageFixtures } from '@/utils/test/fixtures/language';
 import { installUserFixtures } from '@/utils/test/fixtures/user';
 import {
   closeInMongodConnection,
@@ -43,7 +44,7 @@ import { RoleRepository } from '../repositories/role.repository';
 import { UserRepository } from '../repositories/user.repository';
 import { InvitationModel } from '../schemas/invitation.schema';
 import { PermissionModel } from '../schemas/permission.schema';
-import { RoleModel, Role } from '../schemas/role.schema';
+import { Role, RoleModel } from '../schemas/role.schema';
 import { UserModel } from '../schemas/user.schema';
 import { InvitationService } from '../services/invitation.service';
 import { PermissionService } from '../services/permission.service';
@@ -66,7 +67,10 @@ describe('AuthController', () => {
     const module: TestingModule = await Test.createTestingModule({
       controllers: [LocalAuthController],
       imports: [
-        rootMongooseTestModule(installUserFixtures),
+        rootMongooseTestModule(async () => {
+          await installLanguageFixtures();
+          await installUserFixtures();
+        }),
         MongooseModule.forFeature([
           UserModel,
           RoleModel,
diff --git a/api/src/user/controllers/user.controller.spec.ts b/api/src/user/controllers/user.controller.spec.ts
index d7b6504f..041d8e27 100644
--- a/api/src/user/controllers/user.controller.spec.ts
+++ b/api/src/user/controllers/user.controller.spec.ts
@@ -25,6 +25,7 @@ import { I18nService } from '@/i18n/services/i18n.service';
 import { LanguageService } from '@/i18n/services/language.service';
 import { LoggerService } from '@/logger/logger.service';
 import { IGNORED_TEST_FIELDS } from '@/utils/test/constants';
+import { installLanguageFixtures } from '@/utils/test/fixtures/language';
 import { installPermissionFixtures } from '@/utils/test/fixtures/permission';
 import { getUserFixtures, userFixtures } from '@/utils/test/fixtures/user';
 import { getPageQuery } from '@/utils/test/pagination';
@@ -45,8 +46,8 @@ import { RoleRepository } from '../repositories/role.repository';
 import { UserRepository } from '../repositories/user.repository';
 import { InvitationModel } from '../schemas/invitation.schema';
 import { PermissionModel } from '../schemas/permission.schema';
-import { RoleModel, Role } from '../schemas/role.schema';
-import { UserModel, User } from '../schemas/user.schema';
+import { Role, RoleModel } from '../schemas/role.schema';
+import { User, UserModel } from '../schemas/user.schema';
 import { PasswordResetService } from '../services/passwordReset.service';
 import { PermissionService } from '../services/permission.service';
 import { RoleService } from '../services/role.service';
@@ -71,7 +72,10 @@ describe('UserController', () => {
     const module: TestingModule = await Test.createTestingModule({
       controllers: [ReadWriteUserController],
       imports: [
-        rootMongooseTestModule(installPermissionFixtures),
+        rootMongooseTestModule(async () => {
+          await installLanguageFixtures();
+          await installPermissionFixtures();
+        }),
         MongooseModule.forFeature([
           UserModel,
           RoleModel,
diff --git a/api/src/user/services/invitation.service.spec.ts b/api/src/user/services/invitation.service.spec.ts
index e15a2c11..003f605a 100644
--- a/api/src/user/services/invitation.service.spec.ts
+++ b/api/src/user/services/invitation.service.spec.ts
@@ -25,6 +25,7 @@ import {
   installInvitationFixtures,
   invitationsFixtures,
 } from '@/utils/test/fixtures/invitation';
+import { installLanguageFixtures } from '@/utils/test/fixtures/language';
 import {
   closeInMongodConnection,
   rootMongooseTestModule,
@@ -53,7 +54,10 @@ describe('InvitationService', () => {
   beforeAll(async () => {
     const module: TestingModule = await Test.createTestingModule({
       imports: [
-        rootMongooseTestModule(installInvitationFixtures),
+        rootMongooseTestModule(async () => {
+          await installLanguageFixtures();
+          await installInvitationFixtures();
+        }),
         MongooseModule.forFeature([
           RoleModel,
           PermissionModel,
diff --git a/api/src/user/services/passwordReset.service.spec.ts b/api/src/user/services/passwordReset.service.spec.ts
index 0ab45ca3..cdef472a 100644
--- a/api/src/user/services/passwordReset.service.spec.ts
+++ b/api/src/user/services/passwordReset.service.spec.ts
@@ -25,6 +25,7 @@ import { LanguageModel } from '@/i18n/schemas/language.schema';
 import { I18nService } from '@/i18n/services/i18n.service';
 import { LanguageService } from '@/i18n/services/language.service';
 import { LoggerService } from '@/logger/logger.service';
+import { installLanguageFixtures } from '@/utils/test/fixtures/language';
 import { installUserFixtures, users } from '@/utils/test/fixtures/user';
 import {
   closeInMongodConnection,
@@ -49,7 +50,10 @@ describe('PasswordResetService', () => {
   beforeAll(async () => {
     const module: TestingModule = await Test.createTestingModule({
       imports: [
-        rootMongooseTestModule(installUserFixtures),
+        rootMongooseTestModule(async () => {
+          await installLanguageFixtures();
+          await installUserFixtures();
+        }),
         MongooseModule.forFeature([
           UserModel,
           RoleModel,
diff --git a/api/src/user/services/validate-account.service.spec.ts b/api/src/user/services/validate-account.service.spec.ts
index b3ca7753..ac3b2ae9 100644
--- a/api/src/user/services/validate-account.service.spec.ts
+++ b/api/src/user/services/validate-account.service.spec.ts
@@ -22,6 +22,7 @@ import { LanguageModel } from '@/i18n/schemas/language.schema';
 import { I18nService } from '@/i18n/services/i18n.service';
 import { LanguageService } from '@/i18n/services/language.service';
 import { LoggerService } from '@/logger/logger.service';
+import { installLanguageFixtures } from '@/utils/test/fixtures/language';
 import { installUserFixtures, users } from '@/utils/test/fixtures/user';
 import {
   closeInMongodConnection,
@@ -44,7 +45,10 @@ describe('ValidateAccountService', () => {
   beforeAll(async () => {
     const module: TestingModule = await Test.createTestingModule({
       imports: [
-        rootMongooseTestModule(installUserFixtures),
+        rootMongooseTestModule(async () => {
+          await installLanguageFixtures();
+          await installUserFixtures();
+        }),
         MongooseModule.forFeature([
           UserModel,
           RoleModel,
diff --git a/api/src/utils/test/fixtures/language.ts b/api/src/utils/test/fixtures/language.ts
index 8b2f2e44..57d64958 100644
--- a/api/src/utils/test/fixtures/language.ts
+++ b/api/src/utils/test/fixtures/language.ts
@@ -8,10 +8,10 @@
 
 import mongoose from 'mongoose';
 
-import { LanguageUpdateDto } from '@/i18n/dto/language.dto';
+import { LanguageCreateDto } from '@/i18n/dto/language.dto';
 import { LanguageModel } from '@/i18n/schemas/language.schema';
 
-export const languageFixtures: LanguageUpdateDto[] = [
+export const languageFixtures: LanguageCreateDto[] = [
   {
     title: 'English',
     code: 'en',