fdroidserver fails on MacOSX while init

When installed from git, fdroid init fails with key error: keytool in while using code that reads: config['keytool']. I've then tried with MacPorts (which uses python2.7 and not python3 at the time of writing) and it installs. However, it fails the command fdroid init with such error:

erreur keytool : java.util.IllegalFormatConversionException: d != java.lang.String
java.util.IllegalFormatConversionException: d != java.lang.String
	at java.base/java.util.Formatter$FormatSpecifier.failConversion(Formatter.java:4331)
	at java.base/java.util.Formatter$FormatSpecifier.printInteger(Formatter.java:2846)
	at java.base/java.util.Formatter$FormatSpecifier.print(Formatter.java:2800)
	at java.base/java.util.Formatter.format(Formatter.java:2581)
	at java.base/java.util.Formatter.format(Formatter.java:2517)
	at java.base/java.lang.String.format(String.java:2747)
	at java.base/sun.security.tools.keytool.Main.withWeak(Main.java:3151)
	at java.base/sun.security.tools.keytool.Main.printX509Cert(Main.java:3182)
	at java.base/sun.security.tools.keytool.Main.doPrintEntry(Main.java:1995)
	at java.base/sun.security.tools.keytool.Main.doCommands(Main.java:1212)
	at java.base/sun.security.tools.keytool.Main.run(Main.java:397)
	at java.base/sun.security.tools.keytool.Main.main(Main.java:390)

This error is due to my locale (french) where the decimal separator is a comma not a dot. fdroid triggers this command:

keytool -list -v -keystore keystore.jks -alias MacBook.local -storepass:file .fdroid.keystorepass.txt

while it should trigger this command:

keytool -list -v -keystore keystore.jks -alias MacBook.local -storepass:file .fdroid.keystorepass.txt -J-Duser.language=en