What is the ruling on swearing by saying: "By Allah, the Almighty," and is it obligatory to denounce someone who says it, while not being certain of the correctness of their pronunciation of it?

It is not permissible to intentionally distort Allah's name or change a letter from it for someone who is able to pronounce it correctly. Whoever hears that should denounce it and advise its speaker, unless the speaker is unable to pronounce the letter, in which case there is no denunciation or blame upon him.