If a language teacher has taught a topic in the class and no student asks questions in her class, then may be—

When students don't ask questions, it often indicates that the content was beyond their comprehension—they don't understand enough to even formulate questions. Active questioning indicates engagement and partial understanding. Silence may indicate confusion or feeling lost. Good teaching typically generates questions as students engage with new ideas. Assuming excellent teaching or higher learning levels from silence is misleading; lack of questions usually signals comprehension difficulties.