There are many options, and as always which one works for your group will largely depend on the system and the players. So long as everyone agrees to abide by the chosen convention, whichever your group likes is great.
You're already experimenting with colored text, and @JonathanHobbs pointed out the excellent Is there an optimum set of colors for 10 players? thread to help you pick good colors. I'd just like to mention that you run the risk of alienating any colorblind players with this option.
@p.marino covered this in more detail, and I'd like to propose a further simplification:
Dae'eravin: ELV A star shines on the hour of our meeting.
Jack: CMN What? I don't speak Fancy.
In some interfaces it's possible to use a different font for each language. I don't recommend this as it leads to illegible fonts and is easy to confuse unless the fonts are chosen perfectly. You'll also have to use a method that ensures everyone can load all the fonts properly.
A lesser form of the font option is to use italics, underlines, and other formatting options. This probably doesn't offer enough variation to cover your needs, and it places limits on the use of formatting for other purposes.
Bracketing phrases with symbols is another choice:
Dae'eravin: ~ A star shines on the hour of our meeting. ~
Jack: | What? I don't speak Fancy. |
Though you'll want to avoid symbols that are too similar, and cross-platform compatibility problems may crop up if you pick unusual ones.