Hi David, thanks to your suggestion I was able to locate and enable an all-english tiles provider in my custom front-end implementation of Leaflet (so, no need for more pointers!)...
I'm using the Leaflet-providers javascript extension to Leaflet to simplify providers integration and found that several tiles providers do not require an API key and have all-english labels, here are 2 of my favourites:
Esri.WorldStreetMap
CartoDB.Voyager
You can check out more providers supported by the Leaflet-providers js here: https://leaflet-extras.github.io/leaflet-providers/preview/
Anh, you may want to consider switching to one of these in a future release.
Hope this helps!
Mauro.