Multiple-language document - babel - selectlanguage vs begin/end{otherlanguage}

Question

What's the difference in babel package, between :

\selectlanguage{languageA}

and

\begin{otherlanguage}{languageB}
Text in language B.
\end{otherlanguage}

?

I'd like to write two langauge document, where I will have whole chapters in one or another language, each in separated included file.

Which Method of language switching is more appropriate in my case?

Answer 1

The question is if you also want to change the date format and e.g. the chapter headings, when you have chapters. If yes, then use \selectlanguage. If you want to keep the date format and chapter headers like "Chapter", then use the environment otherlanguage* or for a short text the command \foreignlanguage.

Answer 2

The \selectlanguage command and the otherlanguage environment have the same functionality: change all language-related settings; the difference is that the environment defines a group so the language change is local to the environment.

In your case, since the changes must apply to whole chapters, I'd probably go with \selectlanguage, unless intermixing left-to-right typesetting with right-to-left typesetting is required, in which case the environment would be better according to babel documentation:

The environment otherlanguage does basically the same as \selectlanguage, except the language change is local to the environment. This environment is required for intermixing left-to-right typesetting with right-to-left typesetting.

There's also an otherlanguage* environment in which the typesetting is done according to the rules of the other language, but the text-strings such as "figure", "table", etc. are left as they were set outside this environment.