Allow changing of language preference from profile page

cms/envs/common.py

common/djangoapps/lang_pref/api.py

common/djangoapps/lang_pref/tests/test_api.py

common/djangoapps/user_api/api/account.py

common/djangoapps/user_api/api/profile.py

common/djangoapps/user_api/tests/test_profile_api.py

lms/djangoapps/student_account/test/test_views.py

lms/djangoapps/student_account/views.py

lms/djangoapps/student_profile/test/test_views.py

lms/djangoapps/student_profile/urls.py

lms/djangoapps/student_profile/views.py

lms/envs/common.py

lms/static/js/student_profile/profile.js

lms/templates/modal/_modal-settings-language.html

lms/templates/student_profile/index.html