to accept or absorb an idea, opinion, belief, etc. so that it becomes part of your character

He had not expected the people so readily to internalize the values of democracy. 他没有料到人民这么快就接纳了民主的价值观。

If you internalize your emotions or feelings, you do not allow them to show although you think about them.

Many women tend to internalize their anxiety and distress. 妇女常常将所有的焦虑和苦恼都深藏心底。