How do you stay motivated to keep learning a foreign language through the long intermediate stage?

Keep connected to the languages you love through social network, news paper, TV programs...ect

Learn about culture and customs of the country of origin of your language.

Love the language and she will love you too!

I NEVER have the problem ...i like learning languages

I never had such problem - English came to me quite well, and German also, as well as Polish - it all came on me via beginner and then fast to advanced or intermediate levels that are OK with me 

First, determination is what you have to have. Secondly, you have to keep the reason/s  in your mind all the time; why are you learning this?. Thirdly, make an unbreakable promise to yourself that you are going to practice every single day no matter what came up. Finally, get rid of any negative thoughts that may hold you back.

There is a good saying: You change your attitude with a language you speak. 

Any language belongs to a specific culture and cultures vary. I work with people and there is no success until I understand what my customer wants, needs, and expects. If I want to understand my customer, I have to speak his language. But you may become a true connoisseur at vocabulary and grammar, but the point is to be familiar with the culture of a language you speak or study.  

I have a thirst for deep knowledge and bright adventure, I will never obtain what I eagerly work on if I speak my mother tongue only. This is my motivation.