Some BO3 maps are not playable because of your games language. With this work around you should be able to play any map that is not playable due to your game language. I've tested this using the English version of BO3, but this will work for all versions of the game. The easiest way to fix this problem is to change your game language to English, but apparently this is not possible on all versions of the game.
EASY WAY Change Game Language:
Steam Library, Right click on Call of Duty: Black Ops III, Properties, Language, and change it to English.
If you don't have this option to change your language, follow below to get the map to work.
Go to your Steam Library > steamapps > workshop > content > 311210. This is where all your custom maps are installed
Finding The Map
For this example I am using the map Saw 1, which is only playable with the English Version (en) of the game. (To easily find the folder number for your map in the BO3 workshop go to the map page and click share and notice the number at the end of the url.
Change The File Name
To make the map work for your language change these two files to your language code. In this example I've changed this to work with the Russian (ru) version of the game. The map should now be playable.
bp = Brazilian Portuguese ea = (not sure) en = English es = Spanish fr = French ge = German it = Italian ja = Japanese po = Polish (not sure) ru = Russian sc = Sardinian (not sure) tc = (not sure)