So ultimately, what you are asking them for is a raise, pure and simple. I think you need to have a shift in your mindset away from simply citing your specific language skill. That's small potatoes. Step back and look at the big picture. If everyone working as an NP on your unit approaches management with pertinent points regarding the value they bring to the table, you would be up against folks that refer back to their years of experience, production numbers, language skills, patient satisfaction, etc. So being fluent is one of many things that one can point to when asking for a raise. I think if you present it as your only saving grace, you will look like you are straining at ways to make extra cash. I just think you'd look silly and inexperienced if you present language skills as your main case for a raise.
If you are adamant about trying to get a raise, I think you need to present your value on several different fronts. So don't go into a conversation presenting one point. Ask for a raise based on several aspects of what you bring to the table, language skills being just one of several. So when you approach your manager to talk about this, I think you should present it as kind of a recap of where you are as an NP of one year. You could approach it like "I've been part of the team here for a little over a year, and I'm in the swing of things now that I'm getting more comfortable with my role. I'm doing well in X area, as well as X. I've noticed that one of the things that sets me apart is how beneficial my language experience is to the workflow and my production, but also how much time and money it saves us vs. when we have to use translation services. I feel like the monetary value of that is something I'd like to be rewarded for, because its not a skill that everyone has, especially at the level of quality that I bring to the table when I translate based on my ability as a certified translator. So with all these things in mind, I'd like to ask for a raise."
But I wouldn't ask for a raise unless you have something else to point to. They knew about your language skills when they hired you, and you accepted the terms. You are springing this on them after the fact, so you need to have more ammunition than just that. But overall, you are simply asking for a raise. They will likely tell you no, or give you maybe $1500 to settle your request and move on. But you never know until you ask. You bring in lots of money for the hospital, and are a lot more cost effective than a physician, so you don't need to be shy about asking for a raise.
The reason why providers jump around to work at different places is because that's the surest way to maximize negotiating power. Administration never seems to understand the concept of retention to the same degree that they willingly reward those they seek to recruit. My experience as an RN has very clearly shown me that facilities are willing to watch nurses walk rather than put meager effort into keeping them. The reason why is because if they give in and accommodate one employee, they have a whole facility of employees that will also want in on that. But, if they bring someone new in, the administration simply states that the market is shifting and the new hires demand more robust offers. Even if the new hires are more expensive initially, that still is a lot cheaper than the legions of employees that they know will be clammoring for raises if they have to pay to retain what they have. If a handful of folks walk every few months, that's just the cost of doing business. The hospital is counting on most employees staying put. The loyal folks get a meager raise, and their PTO builds up, and they also don't have to stress over adapting to a new place to work.
If your boss knows you are staying put, you will get nothing. If you get anything at all, it will be hardly worth the effort for you, and it will just be a matter of them throwing you some crumbs. Honestly, I'd just simply sit tight and look for other opportunities down the road. I don't thing you are out anything by asking for a raise and cite several aspects of your care that is helpful to the facility. But I wouldn't try to squeeze out a few dimes by going hat in hand to them and asking them for money for translating. I am at a loss to adequately describe why I think you will lose face on that single minded approach, but I just think it kind of comes across as if you are just scrounging for money any way you can. I'm not saying that you are like that, I'm just saying that since you are a provider now, and not a nurse, you should cultivate an image of being above that. Either ask for a raise regarding a number of skills you bring to the table, or just work hard and look around for a different job. When you do find a different job, you come at the new job with a demand for a higher wage than you have. When you have that tied down, then come back to the new place and give them an opportunity to counter if they want to keep you. But don't go beg for some chump change, because its not worth your time. They won't give you more than a fraction of what a translator makes.