What is a proper verb form to use for a Web App?

I’m creating a web app for services like CRM, Helpdesk, etc, and I’m wondering what might be the best verb form to use to address users… Why?

There will be a lot of tooltips, help guides, instructions, etc, and most importantly…command buttons and different verbal terms can be used…

For Romanic languages, the verb form changes, significantly. While in English, this is not problematic because the conjugating the verb form ‘Save’ is quite simple and eliminates the problem.

Save (infinitive), Save (You), Save (The formal pronoun for You)

In Romanic or Latin languages, this is up for a big debate due to the use of the formal pronoun for YOU. In this case, the conjugated form of the verb Save = Guardar is:

Guardar (Infinitivo), Guarda (Tú), Guarde (Usted).

As we’ll be addressing different audiences that cross over different ages, what do you think is the most correct and most common used form?

My idea is to simply use the “infinitive” but I’d like to get your feedback on this.

Are there any alternatives? Or maybe a post reviewing this issue?

Thanks!