It is worth noting that the unintelligible accent issue is context dependent. A native English speaker can be the person with an unintelligible accent, and that person may need to work on their communication skills in order to have influence.
I experienced this phenomenon first hand as a native English speaker with an Australian accent. At my first hostel abroard there was a mixed group of european (non UK) people conversing in English, and I thought I'd try and join in.
me: howrya?
group: blank stares
me: how are you?
group: blank stares
me: how - are - you?
group: look of fear
me: hello?
This first experience was definitely a shock, and it took me some time to realise what it must have been like for the group.
In terms of learning to understand native speakers, travelling in their country for an extended period seems to work. My family has hosted many international guests through exchange programs, including adult guests who had never left their home country (but were taught English at school). Communication was sometimes very difficult, but universally the guests were able to pick up on the Australian accent over time. When exchanges move from blank looks to questions about particular words used, you can start having clunky conversations.
The exchange programs did give our family tips on how to converse with the guests. The only tip I can remember is to try and use different words. Often the longer and fancier word (e.g. gigantic, massive) is easier to understand for the guest than the short and simple word (e.g. big).
I experienced this phenomenon first hand as a native English speaker with an Australian accent. At my first hostel abroard there was a mixed group of european (non UK) people conversing in English, and I thought I'd try and join in.
me: howrya?
group: blank stares
me: how are you?
group: blank stares
me: how - are - you?
group: look of fear
me: hello?
This first experience was definitely a shock, and it took me some time to realise what it must have been like for the group.
In terms of learning to understand native speakers, travelling in their country for an extended period seems to work. My family has hosted many international guests through exchange programs, including adult guests who had never left their home country (but were taught English at school). Communication was sometimes very difficult, but universally the guests were able to pick up on the Australian accent over time. When exchanges move from blank looks to questions about particular words used, you can start having clunky conversations.
The exchange programs did give our family tips on how to converse with the guests. The only tip I can remember is to try and use different words. Often the longer and fancier word (e.g. gigantic, massive) is easier to understand for the guest than the short and simple word (e.g. big).