welcome to the notepad++ community, @Cesare-Pavin
i think we might need more information.
please go to ? > debug info... > copy debug info into clipboard and paste your debug information here, as all versions from 7.6 to 7.6.4 may eventually cause encoding problems.
if you are on 7.6.6 or 7.5.9 and lower:
open up any existing, working vbscript file with umlauts in windows notepad.exe and check if all umlauts are shown correctly.
if they are, open this file in notepad++ and check if all umlauts are shown correctly.
if your umlauts are shown correctly in notepad++ as well, go to the notepad++ menu encoding and check which encoding has a bullet.this will be your correct encoding. (usually either utf-8, ansi, or windows-1250) if your umlauts are not shown correctly, try to set another encoding from the encoding menu.