A portable version of the game would not require installation. The language files should be placed in the same directory as the game executable.
You can check the Steam store for Total War: Attila and see if there's an English language pack available for download. Sometimes, the game and its language files are bundled together. i total war attila english language files downloadl portable
You're looking for a download link for the English language files for Total War: Attila, specifically a portable version. Here are a few options: A portable version of the game would not