If someone pretends to not know English in order to fit into a certain environment it doesn't mean he's unprofessional. When an actor in a movie acts dumb (ie. most famous example Mr.Bean), does it mean he's actually dumb? No. Every single Agent that is not undercover represents FBI in a professional manner. We won't enforce them to be professional and speak proper English when they go undercover simply to allow them to fit in into the environment they are targeting. If one has to join a mexican gang, he has to use mexican slang and wording.
Roleplay:
What's so much different from pretending to be someone and acting to be someone?
This is the difference:
Because, and this is just my opinion, writing "bad English" on purpose requires skill in how languages work. If the FBI agent goes undercover as a Russian noob, the agent needs to have knowledge of how the Russian language is written (not necessarily know the language, just how subjects, verbs, plurals, etc interact with one another) and then purposefully write English in a way a typical Russian foreigner inexperienced in English would write. That is called acting.
Lazy English on the other hand is just typing in "internet language" and in my opinion abuses the fact that this is a text-based RPG.
Right now the UC feds encountered are using "lazy English". Instead of simply being
bad at English, they type in standard internet language (such as 'u' instead of 'you', etc) rather than roleplaying having bad English. This abuses the fact that we're in a text based game, as the difference of 'u' and 'you' only exists in written form, not in speech. You do not need to type like a 12 year old on Runescape for people to accept your English as bad, convince them you're a foreigner with your roleplay instead.
That's the difference between professional and unprofessional. What's next, will your agents start typing in l33t5p35k?