I wanted to ask why exactly we aren't alowed to run the germam version of the game beacause i wanted to start speedrun this game and i can't speedrun it beacause i only have the german version of pokémon black 2/ white 2

Having to play in English to appear on the main leaderboard is a rule that has existed since Red's first Any% Glitchless record in 2008. This allows a total speed equality in all dialogues, in all games of all generations, from the first to the 8th.

Moreover, absolutely all guides, all documentation, as well as all discussions about Pokémon speedruns on its discord are done in English. Due to the constant use of proper nouns in these (pokémons, attacks, towns) using a different language to make a speedrun is, without a doubt, counterproductive.

Here's why only English has always been allowed in leaderboards. The only exception being the Japanese, since Red's any% Glitchless rules split, because of the Pokédoll Skip.

So, I advise you to get an English version of the game in order to speedrun it. Thus, you will be able to keep all the pokémons of your German cartridge! (: