As far as I know the app uses the same language as your phone. Your phone is in ?

This page says that Dutch is not available, that's maybe why it uses Spanish instead.

https://eurail.zendesk.com/hc/en-001/articles/7542797505949-How-do-I-change-the-language-on-the-app-

You may prefer German or English.

My phone is in Dutch.

I cannot find any setting where i can select English or German and not Spanish.

On mobile you can use the Google Translate App to translate text in another app.

I just tried it and it does work.

https://support.google.com/translate/answer/6350658?hl=en&co=GENIE.Platform%3DAndroid

I hope that link works.

If the link doesn't work I just asked Google "can google translate an app".

Hope this helps you.

EDIT: on that page that thibcabe linked it does suggest disabling any autotranslation apps but I have checked the settings instructions in the link and railplanner wasn't listed.

Might be best you submit a ticket if you still can't change the language.

As a display language, the app uses the first language it knows in your list of system languages. If the phone is in Dutch and the app is in Spanish, then it looks like Spanish is listed high in that list, possibly just below Dutch.

This is annoying though. You should be able to choose the language of any app yourself, so that you can have each of them in the source language: the rail planner app in English, DB in German, SNCF in French etc. That way you avoid funny/incorrect translations, such as "Anschrift” (instead of Richtung) in the German version for Direction...

I've already asked a few times to have a language selection in the rail planner app but that still hasn't been implemented. @Mukhammad, do you know what has become of the enhancement to this effect mentioned in ticket #417556?