fix(auth): persist user locale on signup and oauth login

[AritraDey-Dev]

What does this PR do?

• Fixes Non Persistent Multi Language #19646 (GitHub issue number)
• Fixes CAL-XXXX (Linear issue number - should be visible at the bottom of the GitHub issue description)

Visual Demo (For contributors especially)

Before:

Screencast.from.2026-02-15.21-11-22.webm

After the fix:

Screencast.from.2026-02-15.20-20-15.webm

This PR ensures the website always stays in your preferred language by saving your language choice to the database when you sign up or log in.

A visual demonstration is strongly recommended, for both the original and new change (video / image - any one).

Video Demo (if applicable):

• Show screen recordings of the issue or feature.
• Demonstrate how to reproduce the issue, the behavior before and after the change.

Image Demo (if applicable):

• Add side-by-side screenshots of the original and updated change.
• Highlight any significant change(s).

Mandatory Tasks (DO NOT REMOVE)

• I have self-reviewed the code (A decent size PR without self-review might be rejected).
• NA
• I confirm automated tests are in place that prove my fix is effective or that my feature works.

How should this be tested?

Sign up or log in via OAuth with a specific browser language and verify that the UI language persists even after subsequently changing your browser's language settings.

[cubic-dev-ai]

2 issues found across 3 files

Prompt for AI agents (all issues)

Check if these issues are valid — if so, understand the root cause of each and fix them. If appropriate, use sub-agents to investigate and fix each issue separately.


<file name="apps/web/app/api/auth/signup/handlers/calcomSignupHandler.ts">

<violation number="1" location="apps/web/app/api/auth/signup/handlers/calcomSignupHandler.ts:231">
P2: Existing invited users updated through the upsert path never get the new locale persisted; locale is only set in `create`. Add `locale: userLanguage` to the `update` clause so completing signup updates locale for existing users.</violation>
</file>

<file name="apps/web/app/api/auth/signup/handlers/selfHostedHandler.ts">

<violation number="1" location="apps/web/app/api/auth/signup/handlers/selfHostedHandler.ts:140">
P2: Locale is only set in the upsert create branch; existing users updated via invite flow never get their locale persisted. Add locale to the upsert update payload to save language for pre-created/invited users.</violation>
</file>

_{Reply with feedback, questions, or to request a fix. Tag @cubic-dev-ai to re-run a review.}

[romitg2]

@AritraDey-Dev can you please check cubic comments

[AritraDey-Dev]

@romitg2 i think i’ve already resolved them in the next commit. am I missing anything?

[romitg2]

@romitg2 i think i’ve already resolved them in the next commit. am I missing anything?

oh sorry, then it's fine. could you add before video, just to be sure that issue is still reproducible.

[AritraDey-Dev]

@romitg2 i think i’ve already resolved them in the next commit. am I missing anything?

oh sorry, then it's fine. could you add before video, just to be sure that issue is still reproducible.

sure! added in the PR description.thanks