I can't imagine a time where it would be acceptable for students to turn in work with all of those abbreviations. This might be fine in an informal setting, but I wouldn't accept a student's work written that way. It is our job as teachers to show them how to speak and write in conventional English beginning in the early grades. The kids need to recognize the difference in formal and informal writing and when to use one over the other.

I think there are so many shifts that are hard for me to take.  With the Gutteburg Press, we shifted to a print culture, which helped foster democracy, but also led to imperialism. Yet, we still held on to the oral culture as well.  In the late 1800's, with the invention of the light bulb, the photograph and the telegraph, we began the early shift to an image culture.  We lost most aspects of the oral culture, but we retained much of the print culture.  As we now move to a digital culture, we will probably keep the image culture (with tv and movies) but lose most of the print culture.  

As far as yourself learning txt, IM and L33T, I would check out the more common ones that your student population uses, just so you can spot check the social situations of the kids. UrbanDictionary.com can be fairly useful.

I would never accept an assignment w/txt or IM abbreviations or L33T speak unless it was a creative writing assignment and it was crucial dialogue and the student displayed an appropriate knowledge level of Standard English.  Standard English is still how you get a job and function in the work place--at least for a few more years;)  It is key to teach the students when which style of English is appropriate.  Code-switching is a major life skill that everyone should have experience w/ before graduating from high school. Each field has language specific to it that you wouldn't necessarily use when you were talking to someone outside that field. I can gurantee you that your local drug dealer/barista knows just enough slang to get along w/each of the different populations he/she sells to. Students need to know when to say what and to who(m?) to say it. That's why, no matter what the student's base language is, we need to instruct them in Standard English.

How much you as an individual teacher want to learn of each language you come across in your student population is up to you.