(ios) Update localizations

[robbiehanson]

Existing translations updated for iOS.

The following commands were run:

langtool translate --source ios --lang fr
langtool translate --source ios --lang es
langtool translate --source ios --lang cs
langtool translate --source ios --lang ar

Note that we are ready to add translations for all of these languages:
https://developers.deepl.com/docs/resources/supported-languages

[dpad85]

For future localisation PRs, it would be better to split the localisation changes into several commits, 1 for each language updated (within the same PR). It will make the review easier since the localisation resources are all in the same file on iOS.

I also fixed a few strings in the French localisation and I've noticed that DeepL chose to use a more informal tone for the translation (https://en.wikipedia.org/wiki/T–V_distinction), which does not work well in this setting. I suspect it did the same for the other languages. The lang tool should be updated to use the prefer_more option for the DeepL formality setting (see https://developers.deepl.com/docs/api-reference/translate), so that we get a more formal localisation.