WP Residence provides two types of maps. You can choose between Open Street Map and Google Map.

Open Street Map

For the Open Street Map option you don’t need API key. For tiles server (map images) you can use MapBox API optionally.

If you don’t add API for MapBox we will use the default open street server tiles.

To set Open Street as map navigate to Theme options > Map > Map Settings section.

You can get the MapBox API Key from here: https://www.mapbox.com/

Note: Street view and places options from property page map are not supported by Open street map.

How to change Open Street Language

First you need to check this link http://leaflet-extras.github.io/leaflet-providers/preview/ to find the correct language code.
Next apply in code updated based on the language.
The code is in 2 places if you use only Open Street (not mapbox)
wpresidence/js/openstreet/google_map_code_listing_openstreet.js
wpresidence/js/google_js/maps_base.js 

Google maps

To enable Google Maps to navigate to Theme options > Map > Map Settings section and select google maps for Map type option.

Also, you must add your own API Key.  This is mandatory. Help article about how to create API Key for Google map