<!-- IF L_VARIABLE_NAME
This approach will never work, since language constants are only substituted when being found as
, since they're not expected to be handed over via
...is also prone to fail if the text itself contains apostrophes or character sequences which will be interpreted by JS.
The overall approach is questionable, since you hardcode a specific language into the template file(s) of your style(s). To get what you want you're doomed to augment the template parser. An alternative approach (always loading English at first) would impact performance.
The best solution is to maintain the language files. Which is... obvious.