Here's a scenario; a few years ago, you lived in Turkey and got yourself up to a proficient level of Turkish. Far from fluent, you've spent a lot of time trying to keep up the level that you have, but it's been difficult considering you no longer have Turkish people to practice with. You want to get even better, you love being able to speak it, but for now you want to focus on learning Spanish for both your job and travel. Once you get up to a decent level in Spanish, you're hoping to return to Turkish.
The question is; since you've learned several languages, how do you keep up on all of them? You know you shouldn't try learning two languages at once, but what about practicing and improving two languages that you already know fairly well?
My current strategy tip for that is to hire tutors to just chat with you once a week or once every couple of weeks. I do Hungarian for an hour every two weeks and it's been keeping that language at a decent B1/B2 level. It's definitely not getting much BETTER, but it's also not dying off. I do Japanese for an hour every week. That one's also keeping afloat at a B1 level or so. I'm pretty sure I'm losing some of my writing skills in both languages (especially in Japanese). If I had more time, I'd want to devote some of my time to watching Anime with Japanese subtitles, which I think would help me do a better job of maintaining my written Japanese.
I'd strongly recommend the same; you've spent so much time on Turkish...if it's an expense you can afford, it's likely worth the $5-$8 every week or two weeks to have someone to chat with and maintain it. Otherwise I think your best bet is finding TV in that language and setting aside routine times to watch it. Then focus the rest of your time on Spanish, reach a level you like, and then switch to maintenance for Spanish and switch to full on studying mode for Turkish.