Hello Carlos,
Yes, you just have to translate the PO (+ MO) files. For standard Paypay, it is in the core Woocommerce translation. For Paypal Express, you have to translate the PO file of the Paypal Express plugin, and the same for the Stripe plugin: also the PO file of the plugin.
For translation, I highly suggest you to use the POEdit software (https://poedit.net) and you can get the file to edit from the “language” folders into every plugins on your site (on your host). After translation, be sure to store you new translation files in the following folders of your site to avoid them being erased when you’ll update your plugins:
https://www.site.com/wp-content/languages/plugins = This is for both the PO+MO translation files of Paypal Express and Stripe
And
https://www.site.com/wp-content/languages/woocommerce (create a new folder “woocommerce” and put your PO and MO file inside).
Also be sure to correctly name your PO and MO files in order for WordPress to recognize them. As I use French, here are the examples of the name of my files:
woocommerce-fr_FR.po + woocommerce-fr_FR.mo = for Woocommerce core translation
For plugins:
woocommerce-gateway-paypal-express-checkout-fr_FR.po + woocommerce-gateway-paypal-express-checkout-fr_FR.mo
woocommerce-gateway-stripe-fr_FR.po
woocommerce-gateway-stripe-fr_FR.mo
Hope it helps!