I am getting the following Error pointing one of my Xib. This happens after running in Xcode 10. Please help me on this.
Companion strings files can only be specified for base-localized documents. The output path directory does not end with Base.lproj.
The localisation workflow has changed in Xcode 10. You can find a lot of Videos about it here.
In your specific case the problem is that Xcode does not support localisable strings in combination with xib files without base localisation anymore. You will have to convert the strings to a "interface builder cocoa touch xib". You can change this in the interface builder and Xcode will automatically convert the file. 
If you love us? You can donate to us via Paypal or buy me a coffee so we can maintain and grow! Thank you!
Donate Us With