When the characters shout, they are supposed to be speaking GermanAccents and strange patterns of speech are used in Allo Allo to denote when characters are supposed to be speaking other languages. This is mainly used for humor, of course, as the "accents" are stereotypical patterns of speech. I think that when Helga screams COME IN HERE! or the Germans shout or sound loud and nasty, they are meant to be speaking German. German characters are the only ones shown doing this although on a couple of occasions Rene and Madame Edith shout at German soldiers while in disguise. Living in a border area, it would not be unlikely Rene and Madame Edith would know a little German.
Captain Bertorelli's troops speak German.It is unlikely the German army would speak Italian as it wasn't as major a superpower as Germany, and German was considered a more popular language. When Gruber commands Bertorelli's troops he speaks to them in German.
Bertorelli speaks German to the German army.It is possible they are speaking in French, since they're in France, and Bertorelli is certainly able to hold a conversation in French. French was also a popular language then. But as he's helping the German army, it is likely he would be speaking in German to them. He can also eavesdrop on them speaking in German, so he certainly understands the language. That would mean Bertorelli is the most fluent character on the set, apart from Hans (who speaks German, French and English).
Helga and Gruber married each other out of convenience.We know Helga likes rich, powerful men. Gruber who is gay is certainly not her type. And he is not keen on girls. But at the end he becames a successful owner of an art auction-house, so I presume that's why she married him.
Helga is using Herr Flick as a sex object.She finds him boring, rolling her eyes when he insists on making her stay to do boring Gestapo things like Gestapo Monopoly. Even she says she finds him exciting you can see she's lying. When the General tells her to marry Flick she dreads the prospect and even looks forward to going to a love-camp full of the best "German manhood." Yet she will ask him "May I kiss you?" and does it so enthusiastically, while he remains still. Every time he won't let her kiss him she seems to be genuinely upset. Helga is obviously deprived of nookie and is using Herr Flick as something to satisfy her instincts. She's not looking for long-term commitment, because he is boring and he embarrasses her.
von Smallhausen lied about his qualifications to get into the Gestapo.In one episode Herr Flick asks him to decode a Resistance message on the radio, which uses English nursery rhymes. Von Smallhausen says he knows the rhymes, as he went to Oxford. That would mean he would be fluent in English. But in another episode, he decides stupidly to disguise as a British airman by holding a cricket bat. In the end he says "Fafafafafafafa" in order to fool the French into thinking he's British. Why couldn't he just use normal english phrases? Which means he is not fluent in English. He pretended to get into Oxford so the Gestapo would be impressed. his knowledge of English must extend to nursery rhymes.
Helga and Gruber are each other's cover.Gruber is gay, while Helga is an unmarried woman who likes kinky, premarital sex and doesn't seem to have much interest in people who are actually interested in her. Both of them are hardly considered acceptable in the 1940s. The two of them, however, are exceptionally close friends, especially after the war, and so decided to marry each other so they could pursue their own lifestyles without arousing the suspicion of anyone who knew. And if Helga had a few children from her lovers, well, that would just solidify their story even further. The two of them come to love each other very dearly, although not in a romantic or sexual sense, and the children Helga has, Gruber loves as if they were his own.