My website mainly targets international users, and I know most people in international countries know English. However, I try to put myself in their shoes, for example, if I lived in Spain I think I would prefer to read Spanish websites over English ones so; this is why I'm thinking adding localization to my website would be a good feature to include for future growth.
The best way is that you validate the search volume for the relevant queries in the different languages that you're considering to enable a new version for. By doing a keyword research you'll identify how many people search for your services / products / topics in Spanish from Spain or in English from the US and if it compensate to enable a new version to target them specifically. I have shared the process to follow here: https://blog.kissmetrics.com/how-to-international-seo/.