There are some similarities between a newly acquired language and the language you have already spoken. A science article Why your brain just can't remember that word gave some insights on tip-of-tongue experience, especially for people who are bilingual. And I believe it applies to language learners as well. From the article:
One possible explanation is that similar-sounding words compete for our brain's attention. Since bilinguals know twice as many words as monolinguals, there's more chance for tip-of-the-tongue experiences. Since bilinguals, by definition, speak two languages, they are bound to use many individual words less frequently than monolinguals.The key issue is right there. If we use a word less frequently, we tend to have this experience. And it applies to language learning. When we use a newly learned word all the time, and even it is a rather complicated word, we will remember it. But for less frequently used words, they are easily forgotten.
To activate a second language is to use it as often as possible, even when you are talking to yourself.
april
www.mslmaster.com