feat: Add French language

[antvgr]

Description

Add french translation to all pages except news.

Checklist

• Check the License of new pictures (non-commercial use without attribution)

The content was modified in the following languages:

• English
• German
• French

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[MoritzWeber0]

Hi @antvgr! Thanks for the effort to support the FIP Guide and making it available to a larger crowd by adding the French language ❤️

I ran the pre-commit hooks (these are Git hooks to apply some basic formatting locally) and it removed all trailing whitespaces. We decided to use backslashes (\) instead of two trailing whitespaces since trailing whitespaces are hard to recognize in text editors. I can recommend to set up pre-commit on your local device, instructions are available in our CONTRIBUTING.md.

Currently, the news overview on the main page is broken too - I'll have a look at it in the next few days.

[MoritzWeber0]

I tried to fix all formatting issues, but it's probably worth checking all pages again.

Main open topics until it can be merged:

• Translations for news articles is missing (files in content/news)
• Some pages don't use expanders for train categories. We should ensure consistency here.

[lenderom]

I will continue my review later

[lenderom]

From my side I'm finished with the review