[docs] wrote i18n issue template
# What does this PR do?
Makes the issue template for translation- `i18n.md` available. Thank you @omarespejel https://github.com/huggingface/transformers/pull/17004

Some questions:
- Would you prefer a `.yml` format for templates? I can convert it if you wish, @sgugger.
- What labels should be added to the issue? `docs`, `i18n`, `help-wanted`, `WIP` perhaps?

Part of  https://github.com/huggingface/transformers/issues/20183, an effort to update the translation guide.

## Before submitting
- [ ] This PR fixes a typo or improves the docs (you can dismiss the other checks if that's the case).
- [x] Did you read the [contributor guideline](https://github.com/huggingface/transformers/blob/main/CONTRIBUTING.md#start-contributing-pull-requests),
      Pull Request section?
- [ ] Was this discussed/approved via a Github issue or the [forum](https://discuss.huggingface.co/)? Please add a link
      to it if that's the case.
- [ ] Did you make sure to update the documentation with your changes? Here are the
      [documentation guidelines](https://github.com/huggingface/transformers/tree/main/docs), and
      [here are tips on formatting docstrings](https://github.com/huggingface/transformers/tree/main/docs#writing-source-documentation).
- [ ] Did you write any new necessary tests?


## Who can review?

Anyone in the community is free to review the PR once the tests have passed. Feel free to tag
members/contributors who may be interested in your PR.
Hello @sgugger, may you please review this PR?
The docs for this PR live [here](https://moon-ci-docs.huggingface.co/docs/transformers/pr_20199). All of your documentation changes will be reflected on that endpoint.<|||||>> Thanks a lot for drafting this! I think the `WIP` label is fine, it would avoid the issue getting closed by the stale-bot.

Ok, adding it in. So resulting lables will be `WIP` only.<|||||>The docs for this PR live [here](https://moon-ci-docs.huggingface.co/docs/transformers/pr_20199). All of your documentation changes will be reflected on that endpoint.