If you are a UK citizen who lives in or is moving to Spain, it makes life a lot easier if you can speak Spanish. Even if you are a fluent Spanish speaker, you may still be uncomfortable with using the language for complicated financial matters such as insurance.
Two leading Spanish insurers who target UK expatriates have each set up web sites and documentation in English. ASSSA has 70 years experience in health insurance, while Aresa has forty.
They both provide a range of packages for those who live in Spain and are happy to be treated there. If you travel a lot in other countries then they may not be suitable.
If you live partly in Spain and partly in the UK, you may want the option of being treated in the UK. If this is the case you may want to consider the leading Spanish insurer, Sanitas, which is owned by Bupa, and offers documentation is in English.