Well, firstly you need the US to actually have an official language to start with...
But one problem is that while Germans were in the US from colonial times (and got a big boost around 1848), large-scale Italian immigration is much more recent (late 19th/early 20th centuries).
Yep. There is no official language of the US, mostly because the need has never come up because English is so dominant.
In order to make any language, that isn't English an official language at the Federal level, you'd have to have huge, remote, homogenous chunks of the country speaking German and Italian TTL.
This didn't happen OTL due to the haphazard means of immigration. Even in the German-plurality Midwest, there was always enough ethnic diversity(that is, a German town next to an English Town next to an Irish town next to a Danish town) that made English easier.
Italian is a bigger problem: most Italians settled in cities where they quickly assimilated. You'd have to have an earlier start date for the Italian diaspora for most Italian immigrants to choose agriculture over industry.
So, in order to do this, you need:
-An earlier Italian Diaspora.
- Something preventing most Europeans except Germans and Italians from settling in the American Interior: IE, other European gov'ts refuse to allow mass emigration or the US government refusing to allow mass immigration from countries besides Italy and Germany(or, perhaps, the Italies and the Germanies).
- Something preventing WASPs and Irish immigrants from settling the interior to the same levels as OTL. Maybe the climate is a bit harsher or the Indians more hostile so settlement of the Interior is an even bigger risk than OTL.