Well, they wanted to show that the Black Panther was foreign pretty much. There isn't really any in-universe explanation. They wanted people to be able to relate to Thanos and Gamora, so they speak pretty fluently. They wanted to show that Wakanda was isolated from the world, so they gave them an accent.
"They wanted to show that Wakanda was isolated from the world, so they gave them an accent."? Dude. Seriously? The entire African continent has a multitude of accents, every country in Europe has an accent, even the Brits. Every single country has an accent regardless of whether English is their native language or not.
The primary audience for the movie was Americans. It was really negligible what accent they were using as long as it wasn't a very common thing to American ears such as the British, Scottish, German, et cetera. There is indeed a very diverse range of accents in Africa, but the selection for this one accent was arbitrary. They could have thrown a dart at the continent and the result would have been fairly similar. Why are guests always trying to fight without even being capable of winning an argument with a kindergartener I'll never know.
And an accent is indicative of... something. Having an accent essentially boils down to not being able to pronounce English sounds as they should be. You understand it perfectly, but it's just not completely perfect. You're fluent, but you don't quite pronounce the words correctly.
The british have an accent, but they had the damn language far longer than the US did. There's no "perfect" way to pronounce English sounds, as language changes depending on the area and how people use it. That's why there's dialects and accents. All those different groups in China aren't speaking Mandarin wrong, they're just speaking it differently, according to their culture. The British aren't bad at English, they just have their own way of pronouncing things.
Actually, America has had the Britishaccent longer. The American accent is what the British used to sound like. The fancy british accent is a relatively new thing.
And there is indeed the correct way to pronounce a word. The pronunciation varies from location to location, but that does not mean that there isn't a correct way to do it. There is a proper way to pronounce the words even if there is a certain amount of variance allowed. To go a little stereotyping, if you say "Herro" instead of "Hello" then you are speaking with an accent that conflicts with being fluent.
The guardians have chips in them that translate any language to other aliens and vice versa, although it doesn't explain Thanos and The Black Order. We could assume they and the rest of the universe has that technology as well unless otherwise shown
And an accent is indicative of... something. Having an accent essentially boils down to not being able to pronounce English sounds as they should be. You understand it perfectly, but it's just not completely perfect. You're fluent, but you don't quite pronounce the words correctly.
And there is indeed the correct way to pronounce a word. The pronunciation varies from location to location, but that does not mean that there isn't a correct way to do it. There is a proper way to pronounce the words even if there is a certain amount of variance allowed. To go a little stereotyping, if you say "Herro" instead of "Hello" then you are speaking with an accent that conflicts with being fluent.