If your data source has a 'languaga' field that indicates the language, you could use IF fields, like:
{IF«language»= "English" "English Text"}{IF«language»= "French" "French Text"}
or:
{IF{MERGEFIELD language}= "English" "English Text"}{IF{MERGEFIELD language}= "French" "French Text"}
or, if you only indicate when the language is, say, French, you might use something like:
{IF«language»= "French" "French Text" "English Text"}
or:
{IF{MERGEFIELD language}= "French" "French Text" "English Text"}

The French Text" & "English Text" can include multiple paragraphs, images, tables, etc.

Note: The field brace pairs (i.e. '{ }') for the following examples are all created in the mailmerge main document itself, via Ctrl-F9 (Cmd-F9 on a Mac); you can't simply type them or copy & paste them from this thread or another website. Nor is it practicable (for the most part) to add them via any of the standard Word dialogues. Likewise, you can't type or copy & paste the chevrons (i.e. '« »') - they're part of the actual mergefields, which you can insert from the 'Insert Merge Field' dropdown. The spaces represented in the field constructions are all required.

__________________
Cheers,
Paul Edstein
[Fmr MS MVP - Word]