The term target language is used to refer to the language that a business or site owner intends to translate their content into. This of course is a way to reach a broader audience than would otherwise be possible and therefore to potentially increase sales and earnings by a huge margin.
When you translate any piece of text, the target language is the language that you want the text to be changed into.
If you have an online business, or if you make money from a website or an app, then one of the huge advantages you have at your disposal is your gigantic audience. If you work online you see – the entire world becomes your market and it is possible to market your products and your services to absolutely anyone with an internet connection.
However while this may be the case in theory, for many of us it's far from the reality and we instead find ourselves promoting our work to only a very small fraction of the available market. Why? Because we only market to English speakers – leaving out some of the biggest nations on the planets and hundreds of other countries. Not smart.
Of course, if you're only marketing your website to a small portion then you're missing out big time and losing a lot of traffic unnecessarily. When it comes to SEO this is of course a little more tricky, but if you're serious about expanding your horizons then you could consider doing a search on a webmaster forum like Digital Point to find a translator who can make a version of your site in another language – if you don't have too many pages then this might not be too expensive. Alternatively, if you have a friend who can help you, then they might be able to translate your site for you for free or for a smaller fee.
Of course, foreigners will be able to read your site as is thanks to the Google translate feature, but without the right SEO or the right content they won't find your site to begin with. For instance, if you search 'make money online' then you'll find something completely different comes up compared to when you search 'hacer el dinero en linea'.
The good news too is that there's probably less competition for 'hacer el dinero en linea' because fewer people speak Spanish and there are more US and UK websites. If you can make a great site targeting that keyword then, in theory it will be easier to get to the top of the SERPs. If nothing else, you can have pages at the top of 20 different SERPs bringing in 20 times the traffic...
In other aspects of online business these marketing opportunities are a lot simpler too – for instance if you have an app then you should make sure right away that you have versions of your promo text in every language, and Google will even translate the fields for you.