In principle, Across is capable of supporting any language. During the configuration, you can select the languages you want to use. This prevents the system from getting cluttered. However, you can add new languages whenever necessary.
Apart from selecting languages, you can also select sublanguages in Across. Besides the country-specific sublanguages (e.g. Great Britain, USA, etc. for English), you can also select the sublanguages Uncorrected and Simplified. The sublanguage Uncorrected can be used for document correction workflows where, for example, uncorrected English of non-native speakers should be translated into "correct" English. The sublanguage Simplified is intended for documents that are written in a language with simplified syntax and specialized terminology (e.g. in the aerospace industry).
Determining the Language Order and Default Sublanguages
The language order determines the order in which the languages are displayed, e.g. when creating projects. Moreover, you can determine which sublanguage is to be selected by default (e.g. English-United States or German-Germany) when selecting a language. To change these settings in the user settings, click Change Order.
As this is a user setting, the configuration only affects your system.