I want to propose an addition to our basic edit forms

1. in CRM_Core_Form -add a property language and in generic preProcess look for this property in the url & set it on the form
2. in any APIv4 calls at the form layer use this value to setLanguage, if exists, on the api call (this is mostly a principle of intent at this stage)

What does this achieve? Basically it allows me to take action in an extension. Currently the MessageTemplate form uses apiv4 to retrieve and save message templates. I can listen to these calls in civi_data_translate_civicrm_apiWrappers and intervene - retrieving the values relevant to the specific language, if appropriate. This is a pretty tough intervention to do without any core support, and fairly simple with a small change to core + an agreement as to how we prefer to use the api going forwards

https://github.com/eileenmcnaughton/civi-data-translate/blob/master/civi_data_translate.php#L187

Next steps - I would look to convert the EntityFormTrait to use apiv4 to create a generic template / model for how this should be done. (I would need to set api version as a parameter on the form as I realise extensions may use this trait for entities with no v4 api as yet.)

@bgm @colemanw @seamuslee @totten