I don't see any problem in putting one Enki word here and there when chatting, just like NPCs do
But I've just learned today that 'Tabei' means 'friend'. I thought it meant 'stranger', which is closer to the Enki race psicology (everybody addressed me like that the first time i was in Ojaveda... 'How can I help you, Stranger' sound way more appropriate for Enkis than 'How can I help you, Friend').
Just my two trias.
Actually, you have to remember that is coming from the merchants who want your business. They have a motive in calling you "Friend" rather than "Stranger". This is a common practice in many cultures. I have had it happen to me in shops in Korea and The Philippines. A merchant who wants to do business with you is going to want you to feel like you are his friend.
Now if I, as a player character, were to call you "Tabei" the first time I've seen you, that would be odd. Unless I'm just overly friendly. More than likely, I would use the proper friendly greeting for a stranger, which is "Grrensholo, Taajho". Just in case you didn't know, Taajho means stranger.
Personally, I like the idea of the languages adding a richness to the RP experience. I think that players just have to use some sense when interacting with others. If you use a basic phrase and someone doesn't understand, then stop using the language and revert to the common tongue. I've found that it actually sparks interest in others who ask if I can teach them some more.
I also like the idea of characters of various races learning some basic phrases. That also happens when you visit a foreign country. When I lived in Germany, I learned some basic German. But I was FAR, FAR, FAR from being fluent. So my German friends, while appreciating my effort to learn their language, would speak to me primarily in English.
I don't really think it's all that odd that a Kran who is frequently in Ojaveda might encounter an Enki who doesn't speak Enkien. Think about it, perhaps the Enki you encounter isn't from Ojaveda. Maybe they live in another land and they're just newly arrived in Ojaveda. Not everyone of a particular race or nationality speaks the language of that race. My family is of German descent, yet I knew no German before I lived in Germany and still don't know much of it.
I don't think it really breaks RP that much. Just RP it as you would act IRL in a similar situation. Does that make sense?