I don't think it's rude or disrespectful to not want to see posts you don't understand.
In theory there is an option in the settings where you can select languages (if you are using an app and can't find it there, look with a browser). The thing is that (as I understand it) this language filter only works if a language is selected for a post. Since the language selection when creating a post is not implemented in all apps and many people don't care, many posts are not tagged with a language and they will slip through the filter. You could deselect "Undefined" and only keep "English" but then you will probably miss a lot of English posts as well.
Not only more readable than A and B but I would argue it's also easier to remember who did what a few sentences or paragraphs earlier since Alice and Bob invoke slightly less generic mental images than A and B. For example one is a woman and the other one is a man, maybe even some person or character you know.
And now that I'm thinking about it, the different gender also makes it easier to keep track of who does what because different pronouns are used (at least in English and many other languages).