Defensive treatment of i18n of edition numbers

[opoudjis]

German document with an edition in metadata is crashing, because there is no German i18n of the edition number.

[opoudjis]

There is an added bug: the ISO-specific YAML file is defaulting to English (no German ISO-specific YAML file is supplied), but an English file must not be merged into the parent non-English isodoc file.

[opoudjis]

I'm going to address that by having a universal list of supported languages, and using that in all child flavours i18n.

[opoudjis]

In downstream flavours, if they don't have an i18n file for the given language, merge parent i18n into the local English file. That means that any locally needed i18n fields still exist (so compilation doesn't scratch), and it prevents parent German from being overridden with local English.

That said, the only proper outcome is to provide a local German i18n file.

[opoudjis]

Need to restrict load_yaml method to current class, else inheriting flavours will never see it. So super in metanorma-bsi needs to trigger ISO load_yaml, not BSI load_yaml.

[opoudjis]

To avoid that behaviour, creating iso_load_file which is specific to ISO i18n, and is not to be overridden by child flavours; any flavour inherited by another flavour will need to do the same. alias_method would also have worked, but would have prevented a child of a child flavour from correct override behaviour.