1. We build the toolbar entries from from vimmenu_T struct Vim gives us.
2. Menu entry names were used as icon identifiers, and mapped into icons
3. When the menu/toolbar are in a different language this breaks down because
the names change.
The quickest fix to get this working is probably the patch above, the correct solution is to properly map Vim icon identifiers into our icons (:h builtin-tools provides the full icon table).
On a side note, it seems clear that we are also missing other features in the toolbar icons, such as the ability to load a custom icon.