feature: localization's first implmentation

backend/prisma/migrations/20260620120000_add_user_language/migration.sql

@@ -0,0 +1,2 @@
+-- AlterTable
+ALTER TABLE "users" ADD COLUMN "language" TEXT NOT NULL DEFAULT 'en';

backend/prisma/schema.prisma

@@ -15,6 +15,7 @@ model User {
   googleId     String? @unique
   facebookId   String? @unique
   name         String
+  language     String  @default("en")
   trialUsedAt  DateTime?
 
   memberships        Membership[]

backend/src/modules/auth/auth.controller.ts

@@ -9,7 +9,8 @@ import {
   Res,
   HttpCode,
   HttpStatus,
-  Get
+  Get,
+  Patch,
 } from '@nestjs/common';
 import type { Response } from 'express';
 import {
@@ -28,6 +29,7 @@ import { RegisterDto } from './dto/register.dto';
 import { CreateOrganizationDto } from './dto/create-organization.dto';
 import { JwtAuthGuard } from './guards/jwt-auth.guard';
 import { LocalAuthGuard } from './guards/local-auth.guard';
+import { UpdateLanguageDto } from './dto/update-language.dto';
 
 @ApiTags('auth')
 @Controller('auth')
@@ -149,6 +151,14 @@ export class AuthController {
     return this.authService.getProfile(req.user.id);
   }
 
+  @Patch('profile/language')
+  @UseGuards(JwtAuthGuard)
+  @ApiBearerAuth('JWT-auth')
+  @ApiOperation({ summary: 'Update user language preference' })
+  async updateLanguage(@Req() req, @Body() dto: UpdateLanguageDto) {
+    return this.authService.updateLanguage(req.user.id, dto);
+  }
+
   @Get('subscription-alert')
   @UseGuards(JwtAuthGuard)
   @ApiBearerAuth('JWT-auth')

backend/src/modules/auth/auth.service.ts

@@ -15,6 +15,10 @@ import { PrismaService } from '../../../prisma/prisma.service';
 import { LoginDto } from './dto/login.dto';
 import { RegisterDto } from './dto/register.dto';
 import { CreateOrganizationDto } from './dto/create-organization.dto';
+import {
+  SUPPORTED_USER_LANGUAGES,
+  UpdateLanguageDto,
+} from './dto/update-language.dto';
 import { JwtPayload } from './interfaces/jwt-payload.interface';
 
 const ALL_PERMISSIONS = [
@@ -179,11 +183,7 @@ export class AuthService {
         data: {
           accessToken,
           refreshToken,
-          user: {
-            id: user.id,
-            email: user.email,
-            name: user.name,
-          },
+          user: this.toPublicUser(user),
           organizations,
         },
       };
@@ -343,11 +343,6 @@ export class AuthService {
     };
   }
 
-  /**
-   * Get user profile with all memberships and permissions
-   * @param userId - User ID from JWT token
-   * @returns User profile with organizations and permissions
-   */
   async getProfile(userId: string) {
     try {
       const user = await this.prisma.user.findUnique({
@@ -516,11 +511,7 @@ export class AuthService {
         success: true,
         data: {
           accessToken: newAccessToken,
-          user: {
-            id: session.user.id,
-            email: session.user.email,
-            name: session.user.name,
-          },
+          user: this.toPublicUser(session.user),
           organizations,
         },
       };
@@ -931,4 +922,44 @@ export class AuthService {
       },
     };
   }
+
+  async updateLanguage(userId: string, dto: UpdateLanguageDto) {
+    const language = dto.language;
+
+    if (!SUPPORTED_USER_LANGUAGES.includes(language)) {
+      throw new BadRequestException('Language must be one of: en, fa, nl');
+    }
+
+    const user = await this.prisma.user.update({
+      where: { id: userId },
+      data: { language },
+      select: {
+        id: true,
+        email: true,
+        name: true,
+        language: true,
+      },
+    });
+
+    return {
+      success: true,
+      data: {
+        user: this.toPublicUser(user),
+      },
+    };
+  }
+
+  private toPublicUser(user: {
+    id: string;
+    email: string;
+    name: string;
+    language?: string | null;
+  }) {
+    return {
+      id: user.id,
+      email: user.email,
+      name: user.name,
+      language: user.language ?? 'en',
+    };
+  }
 }

backend/src/modules/auth/dto/update-language.dto.ts

@@ -0,0 +1,14 @@
+import { ApiProperty } from '@nestjs/swagger';
+import { IsIn, IsString } from 'class-validator';
+
+export const SUPPORTED_USER_LANGUAGES = ['en', 'fa', 'nl'] as const;
+export type SupportedUserLanguage = (typeof SUPPORTED_USER_LANGUAGES)[number];
+
+export class UpdateLanguageDto {
+  @ApiProperty({ enum: SUPPORTED_USER_LANGUAGES, example: 'en' })
+  @IsString()
+  @IsIn(SUPPORTED_USER_LANGUAGES, {
+    message: 'Language must be one of: en, fa, nl',
+  })
+  language: SupportedUserLanguage;
+}