Since you cannot skip cutscenes in this game, you will have to mash through all the text instead. Unsurprisingly, different languages result in a different amount of textboxes throughout the game, making some languages technically faster than others. Here is an overview for the amount of textboxes per language:

Naturally, Japanese is technically the fastest with 20+ textboxes less than any of the European languages. For an Any% run, Italian has a whopping 1(!) textbox less than English and is therefore the fastest. For completion categories that include the ending cutscene, English and Italian are tied. German has the most textboxes all around. Of course, realistically speaking, this will never really factor into the final time of a full run but it's nice to have this documented.

EDIT: Since you can just soft reset during the ending cutscene in completion categories in order to skip the credits, the Any% textbox totals apply to those as well.