Hi Dan,
first you should try restart IIS application pool for your website (saving web.config file unchanged will have same effect) and clear local browser cache for the domain) to make sure, your changes become effective.

If this doesn't help you may re-enable "en-US" in table portallanguages (it's the record where culturecode is Null). Make sure there is a record in table PortalLocalization for your PortalID with CultureCode=Null as well.
Clear Browser Cache and restart application again afterwards for database changes to become effective.

Thank Sebastian 

Non of these worked for me. I am unable to upload images of my db so I'll try to descibe them

Table Langauages

LanguageID    CultureCode    CultureName    FallbackCulture
1    en-US    English (United States)    en-GB
2    en-GB    English (United Kingdom)    en-GB

Table PortalLocalization

PortalID    CultureCode    PortalName    LogoFile    FooterText
0    en-US    CropDMS     logo.jpg    Copyright [year] by 

Table PortalLanguages

PortalLanguageID    PortalID    LanguageID    CreatedByUserID
2                                     0                1                         1

I am using a different browser for testing and I've restarted the app pool and IIS services

Thanks

Dan

I don't know what version of DNN you are using, but there should have been a record for en-GB in portal localization.
I would try changing the one for en-US to en-GB (and restart the site etc)