merge method
Implementation
void merge(StringResources other) {
for (var lang in other.languages) {
var otherResources = other.getLanguageResources(lang)!;
if (_resources.containsKey(lang)) {
var resources = _resources[lang]!;
for (var key in otherResources.keys) {
resources[key] = otherResources[key]!;
}
} else {
_resources[lang] = otherResources;
}
}
}