The Language section includes properties related to languages and cultures.
The GEDCOM Language property determines which strings (words and phrases) are used when interpreting TMG sentence structres. The default value is "English (United States)".
The Sentence Language property determines which set of sentence structures in the TMG project are used when formatting Note and Text values. The default value is "English (United States)".
Usually, the GEDCOM Language and Sentence Language will be set to the same value. In some cases, TMG users have created custom languages for sentences, and the properties will have different values.