Hi Letizia, That is a great question. You can write emails in specific languages and then setup a diamond to filter contacts into their correct language sequence. As for the Default Merge fields it would only display what is under the Marketing > Settings > Template Default > Merge Fields
However, any external pages would show the languages set through the Contact’s browser. Here is more information on that
https://help.infusionsoft.com/supported-languages-for-external-pages
This guide explains how the browser will capture the language and timezone through the browser settings specifically.
https://help.infusionsoft.com/release-notes/august-update-2016#timezone