If it is for blocks of text then you could use #+BEGIN_VERSE in combination with #+ATTR_HTML, or possibly create a custom #+BEGIN_FRENCH block type, but I suspe

If it is for blocks of text then you could use #+BEGIN_VERSE in combination with #+ATTR_HTML, or possibly create a custom #+BEGIN_FRENCH block type, but I suspect that you are thinking about inline markup, in which case you have two options, one is to write a macro {{{lang(french,ju ne parle frances}}} and the other would be to hack the export-snippet functionality so you could write @@french:ju ne parle frances@@ and have it do the right thing when exporting to html. The macro is certainly easier, and if you know in advance what languages you need it shortens to {{{fr:ju ne parle frances}}} which is reasonably economical in terms of typing.