Your question deals with several topics:

I) As you already noticed: hard coding something in HTML is very unflexible. You should avoid that.

II) The values of your select represent a list of data. The place to keep your data is typically some knd of database. The format you store it in is the canonical form for your application (whatever language you use internally).

III) Outside of your application, you use an internationalized representation of your canonical form. That involves somewhere a translation-step in your rendering pipeline.

[Tutorial for Spring Boot][1]

Where you store the translated strings is up to you and your application; the common way is properties. [1]: https://justinrodenbostel.com/2014/05/13/part-4-internationalization-in-spring-boot/

Your question deals with several topics:

I) As you already noticed: hard coding something in HTML is very unflexible. You should avoid that.

II) The values of your select represent a list of data. The place to keep your data is typically some knd of database. The format you store it in is the canonical form for your application (whatever language you use internally).

III) Outside of your application, you use an internationalized representation of your canonical form. That involves somewhere a translation-step in your rendering pipeline.

Tutorial for Spring Boot

Where you store the translated strings is up to you and your application; the common way is properties.