>I am not aware of the re-usage policy. Someone from WMF team should clarify...
Gladly. Our maps terms of use [2] state that we do allow use by third parties, though there is a concern about over-use, so we request that third parties "please respect our limited services and resources.” There are also some specific requests about providing info, in case we need to get in touch with you, and a caveat that: 
 We reserve the right to discontinue or change our service, block or limit certain users or applications, or take other measures in cases at our sole discretion at any time without notice.

So this is something that may or may not work for you, depending on how large and intensive your map service is. Please have a look at the terms or use if you’re interested in proceeding. 
In answer to Dhaval Sudhanva Vyas’ question about seeing a mix of different languages, Naveen is correct to quote the Special Update on Map Internationalization [3], which is the best source of information on how this all works. I encourage anyone interested to have a look. 
You may also wish to experiment with internationalized maps on testwiki  or testwiki2 [4], where the features are currently working. And here is a page on testwiki2 that shows examples [5]. Later today, I’ll post a deeper dive into how our service interacts with OpenStreetMap data, and some of the anomalies that can arise from that interaction. 
Yours,
Joe

[1] https://www.mediawiki.org/wiki/Map_improvements_2018
[2] https://wikimediafoundation.org/wiki/Maps_Terms_of_Use
[3] https://www.mediawiki.org/wiki/Map_improvements_2018#April_18,_2018,_Special_Update_on_Map_Internationalization
[4]  https://test2.wikipedia.org/wiki/Main_Page or https://test.wikipedia.org/wiki/Main_Page. 
[5] https://test2.wikipedia.org/wiki/Map_internationalization_examples
[6] https://www.mediawiki.org/wiki/Talk:Map_improvements_2018