Language and theme loading and applying should be sync

[altrisi]

Else the website basically flickers from english to the user's language.

Same for dark mode. This one is a lot more visible if you are around the "why iris" section and then reload.

[maxigator]

The lang takes a bit to load because it loads the lang file with fetch api for convenience, but to make it sync all lang data must be in the same file

[maxigator]

There could be a very small loading screen during that