LOL I can understand how some people may find Sera's language foreign and difficult to follow.
That manner of speech is that of South East Londoners, often referred to as "cockneys" and they use cockney rhyming slang that is sometimes incomprehensible by those not familiar with their "dialect".
Sera's is not quite as severe, but that is the background of it. It originates from the part of the population in London that are less privileged and somewhat less educated.
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My credibility? I lived in London (South East) for 5 years.
Not quite - she uses some slang with a cockney accent ('innit' instead of 'isn't it' being a prime example) but most of the time she has a more nothern england accent. Not quite Geordie, not quite Brummie either, just a generic northern inflection.
The 2 things do not mix well, which is why she can be difficult to understand.
It's like reading an Irvine Welsh novel. You have to adopt the accent in your head to understand what is being said. But because she has a blend of two different British accents mixed in with some slang and lazy speech, that's not easy to do even for a native.
I understood her more on the 2nd play through, but still cringe every time she switches accents to get in the 'innit'.