1) Was Fälle betrifft sind einige Sprachen schlimmer. Denk Finnisch, Ungarisch, Koreanisch, Türkisch, die meisten slawischen Sprachen, sogar die italienische Muttersprache Latein hat 6 Fälle.
2) Sprecher besagter sprachen haben meistens kein Problem mit Fällen, sondern eher mit sehr uneindeutigen* Präpositionen.
Also: Einfach ist, was man gewohnt ist. Deutsch hat nur insofern eine interessante Position, weil die ähnlichsten Sprachen um Deutsch herum (germanische und romanische) die Fälle allesamt weitgehend aufgegeben haben.
1) Concerning cases, many languages are tougher (than German). Think: Finnish, Hungarian, Korean, Turkic, most Slavic languages and even Italian's ancestor language Latin features six noun cases.
2) Native Speakers of such tongues usually don't struggle with cases, rather with ambiguous* prepositions
Conclusion: Simple is what you're used to. German only seems weird, because the most similar languages around it (Germanic and Romance languages) all gave up on most cases.
* What I mean is when you translate the same Phrase into different languages, you can end up with very different prepositions: am Teller, on the plate und nel piatto: at the plate, on the plate and in the plate.
Cases are also not 100% identical always, but way closer. for example, I know Latin and German. Latin Ablative and Dative usually correspond to German Dative; Latin and German Accusative mach most of the times too. This system has way fewer exceptions.
It's because "Lingua" is a noun which refers to a language in general. It doesn't follow that a specific language needs to have the same gender. In fact I can't think of a single specific language whose name is feminine in Italian; Italiano, russo, etc. Most languages end in e in Italian (inglese, francese, danese, etc) but if you look them up in a dictionary you'll see that they're masculine. There may be some exceptions to this but I can't think of any at the moment, and certainly not any major languages.
Note: I'm referring to when the language's name is used as a noun in its own right here. If you are using "lingua" as the noun, then the national or regional adjective will still be feminine because of course "lingua" is feminine. For example "Le lingue dell'Italia" (the languages of Italy) refers to the languages and dialects of Italy in general and is therefore feminine. La lingua piemontese refers to the language (dialect) of the region around Torino. However the specific names of the individual languages / dialects are still (as far as I can recall) all masculine, like "Il piemontese".
Consider the similar situation with the masculine noun veicolo (vehicle). It is masculine, but individual vehicle types don't have to be; they can be either masculine (eg il taxi, il tram, il treno) or feminine (eg la bicicletta, la macchina).
In short, it isn't the case that individual nouns have to have the same gender as an "umbrella" noun which groups them together.