I don’t use vimtex, but this looks to be related to the encoding of international characters. In the vimtex getting started, I found this in the requirements:

• UTF8 character encoding enabled (enabled by default in Neovim; place the line set encoding=utf-8in your vimrc).

See :help vimtex-requirements for details on requirements for using VimTeX.

Maybe that could help

In French, “pisse-vinaigre” or vinegar pisser, for someone that complains about everything

I knew about “enculeurs de mouches”, or fly fucker, that is said about a person that is way too picky about useless details