'Allo 'Allo!/WMG

When the characters shout, they are supposed to be speaking German
Accents 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.
 * But in one episode when Helga asks Rene to pose as Himmler, Rene protests he can't because he can't speak German.
 * Strangely enough, Rene understands when he eavesdrops on Herr Flick telling Helga how he plans to kill General von Klinkerhoffen. Presumably the conversation was conducted in 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.
 * One thing bugs this troper. Bertorelli says they are from prisons. Common criminals are unlikely to be fluent in German, a foreign language to them.
 * Maybe they were taught German in the Italian army? After all, they're supposed to collaborate with the Germans.

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.
 * But he did he agree? Possibly to mask his tendencies from his family.
 * Or Helga blackmailed him into marrying her.

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.
 * It's likely she's unable to find a more successful man to marry her. The rest see her as mistress material. Probably she is using him as a possible last option. That could be why she married Gruber in the end.

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.
 * it's not that surprising. We all know him as Engelbert von Smallhausen, but when Herr Flick uses a special fan to make Helga tell the truth von Smallhausen gets in the way, and says his real name is Bobby Cedric von Smallhausen. Presumably he changed it to Engelbert which sounds more mighty and impressive.