In Tinuke Craig’s great production of August Wilson’s classic play, Jitney at the Old Vic earlier this year, the script is written in an American dialect with slang and idioms.  The play is about a group of Pittsburgh taxi drivers.  The detail of the dialogue may be lost sometimes, but the impact and overall sense is massive.  One of the cab drivers eventries to adjust his accent to impress a potential ride.  The Old Vic is a large theatre compared to Leeds Playhouse & the cast had to adjust to the space in the previews, which perhaps accounts for some of the feedback saying it sounded muffled.  The impact of the whole play was improved by the director’s choices.   It’s the director’s decision of when to use an accent to denote the accent and when to make it real. 
Voice coaches are often consulted about scripts and edits, whether it’s from individual actors or the theatre director or assistant theatre director and there is a sense of working together.  A voice coach
can make a big contribution to the overall production success.

Films need to be sold on the market place and I have been given notes by producers to ask actors to make sure their accent is easily understood for a UK and an international English speaking audience.   Dubbing is now so good that it poses no problems to dub into different languages.   
Hampstead Theatre put on a play called Lotus Beauty by Satinder Choan, earlier this year.  The accents and dialects were good, although some members of the audience found it hard to follow the storyline.   One of the characters had recently arrived in Southall and was understood, more by their gestures than their speech

In the TV murder drama, Sherwood by James Graham.  The dialogue is comfortably colloquial and some of the accents more Nottingham that others, but this is in line with the characters’ backgrounds.  The accents around the mining districts of Nottingham, especially around Hucknall are very strong and hard to understand, even for people just outside the area.  In Sherwood, the characters are all played by really good actors, Adheel Akhtar, Lesley Manville, David Morrissey among them, and the drama unfolds without anything jarring on our senses.  Some locals took afront at Nottingham Forest being called Notts Forest, which never happens, but that’s a detail and I’m looking forward to the next series.