Your problem is that the form is failing to save the request sendet by you. See this link: shopware 5.3.4 github
formStore.sync({
success :function (records, operation) {
message = me.messages.saveEntrySuccess;
me.createGrowlMessage(record, title, message);
store.load();
},
failure:function (batch) {
message = me.messages.saveEntryError;
if(batch.proxy.reader.rawData.message) {
message += '<br />' + batch.proxy.reader.rawData.message;
}
me.createGrowlMessage(record, title, message);
store.load();
}
});
To see more details of the problem you will have to activate the debug mode (see shopware documentation on how to do that).
For me it worked to add your locals (English -> Swizerland -> en_CH), however I wonder how will this help me further, because php doesn't recognize this local: php locales list