There is redundant code implementing almost the same logic to check for availability of and trigger manual translation:

(1) Through right-click context menu in https://cs.chromium.org/chromium/src/chrome/browser/renderer_context_menu/render_view_context_menu.cc?type=cs&sq=package:chromium&g=0&l=2189 and https://cs.chromium.org/chromium/src/chrome/browser/renderer_context_menu/render_view_context_menu.cc?l=2642&rcl=de283c850e8c8f099e75341081fd6b246c42e7f0 .

(2) Through clank's manual translation done through TranslateManager::CanManuallyTranslate and TranslateManager::InitiateManualTranslation.

This could be all combined in the idea of triggering a manual translation (basically the unique behavior would be clank's manual translation).