Allow per-language Git repositories

### Describe the problem

I'm considering [switching with Polish translation of Python documentation](https://github.com/python/python-docs-pl/issues/21) to Weblate. Python documentation translations in different languages are being kept in [separate](https://github.com/python/python-docs-zh-cn/tree/3.10) [Git](https://github.com/python/python-docs-fr) [repositories](https://github.com/python/python-docs-pl).

PO files in the repositories are stored in the main directory, without language prefix in directory structure.

"Filemask" field validation in new component form prevents entering a file mask without language code in it, which would be desired in my case. Also after creating a component potentially some other language would like to switch to using Weblate, and then we'd want those translations to land in separate Git repository, not Polish one.

### Describe the solution you'd like

* Allow to by-pass filemask validation for language placeholder in the pattern.
* I think it's ok for me to have a Weblate project per language for case of Python documentation. It would be awesome to have a possibility for having single project with many repositories for different languages. Presumably that can be difficult to implement, as for as far as I know it's not compatible with current Weblate projects architecture.

### Describe alternatives you've considered

I've [forked original Polish Python docs translations repo](https://github.com/m-aciek/python-docs-pl-weblate-poc) and moved all resources to `pl` directory to set proof-of-concept project on Weblate and investigate other parts of integration.
But such a move is not an option to original repository due to the [convention for fetching and rendering the docs](https://www.python.org/dev/peps/pep-0545/#repository-for-po-files).

### Screenshots

### Additional context

[PEP 545 -- Python Documentation Translations](https://www.python.org/dev/peps/pep-0545/)