Language skills are similar to
skills in that there are a huge number of possibilities. They are also
relatively difficult to apply exact rules to.
The following are meant as guidelines, and should not be taken as being written in stone. For example, an illiterate character might have a high language skill (can easily speak and understand others), but just never learned to read or write.
There are situations which may require that a roll be made against a Language skill. For example, professionals of various occupations often have obscure terminology, and a character trying to pass as a member of that profession might have to make a roll in order to understand others of the profession, or speak in such a way that they are accepted by others.
There are similarities between different languages which the GM may wish to take into account at such times as when a character acquires a new language similar to one which is already known, encounters someone speaking in such a language, or attempts to read something written in such a language. For example, French and Italian are similar enough that, for someone fluent in French, many Italian words can be understood through a combination of comparison to known French words and examination of the context the word is used in. Most encyclopedias, and many dictionaries, have diagrams showing how various languages are interrelated. The GM may give a bonus in such situations, depending on the character's skill level in the known skill, and how closely related the two languages are.