I am fluent enough in the Nepali language that I can hold a basic conversation on most topics, and even excel on a few choice topics (mother language education, food, etc.). But speaking in Nepali I just "feel" less intelligent. It takes me longer to parse sentences and longer to respond. I forget words and mix others up and am often laughed at for some amusing mistake. Thinking is just harder to do. It takes longer and it is exhausting. I would estimate that when I speak Nepali I feel about 60% as intelligent as when I speak English (with German I feel about 80% as intelligent and with Spanish I feel about 20% as intelligent).
When I speak Nepali, I am the same person as when I speak English, but the outward manifestation of my personality can be much different. I may be bolder or I may be more shy, depending upon how I face the challenge and constant humiliation of being forced to express myself in a less intelligent (and oftentimes laughably simplistic) way. That is the discomfort and terror of language-learning, and also its exhilarating challenge.
But oftentimes teachers forget this. They teach language as if it were a skill like long division, and not a fundamental means of expressing oneself. They berate their students for not speaking out in class, while forgetting the terror and frustration that they experienced in their own language classes.
And forgetting this truth can have other societal implications as well. It can lead to subtle mental judgments about the intelligence of immigrants or foreigners. When we hear the foreign-accented speech of our own language, we often do not immediately acknowledge that this person is expending a great deal more mental effort to communicate his or her ideas than we are. This person sounds stupid to us even though they are doing something that requires incredible mental stamina and courage.
Coming from a very monolingual society, this is something I need to keep in mind every day that I teach English. The best remedy for that is to get laughed at by a 10-year-old for mixing up the Nepali word for "the day after tomorrow" with the word for "pumpkin."