You need to go in your Shopify dashboard, then select Apps -> ChatX and from the new dashboard menu that you will see on the left, select Settings -> General. Here you have the language option where you can select one of the available languages. 

When you select another language all the static texts displayed on your website will be localized in that language. More than this, our Natural Language Processing will know that the search queries from your website will be in that language and this brings a plus in the performance. 

Another feature that will be affected by the language change will be the voice dictation.