Since commit 7c96f18 TextEditors can’t show horizontal scrollbars, rather, I can’t find a way to show them. Before that commit, setting the TextEditor multiline was more than enough.
In juce_TextEditor.cpp at line 1456, the horizontal scrollbar is always set to false:
viewport->setScrollBarsShown (scrollbarVisible && multiline && (textBottom > viewport->getMaximumVisibleHeight()), false);
Is there a new way to set the horizontal scrollbar?