Grindr currently supports English and Spanish.
In order to change your Grindr language from English to Spanish, please visit Settings > General > Language & Region.
The iPhone Language will always occupy the number one spot in preferred languages.
Under Preferred Language Order, English or Spanish will need to appear first (whichever preference you choose) in order for Grindr to run in either English or Spanish.
In order to change the order, you will need to select Edit in Language & Region and rearrange the order.