No. A language pack does not affect rendering speed, 3D navigation, or calculation times. The string table is loaded into RAM at startup (approximately 5-10MB). The only performance hit is negligible: searching for help files or tooltips might be 2-3 milliseconds slower in a right-to-left language (like Arabic) due to text shaping.
The office manager made a decision: "Install the Japanese Language Pack." archicad language pack work
These new library parts contain translation data for 29 languages. You can change the language of the objects (e.g., changing a door's parameters from English to French) without reinstalling the software. archicad language pack work