alpha character classes in tr do not include all letters of locale

[Jarno Suni]

e.g. [:alpha:] does not include letter å, ä, ö, Å, Ä and Ö of Finnish locale.

ProblemType: Bug
DistroRelease: Ubuntu 16.04
Package: coreutils 8.25-2ubuntu3~16.04
ProcVersionSignature: Ubuntu 4.15.0-46.49~16.04.1-generic 4.15.18
Uname: Linux 4.15.0-46-generic x86_64
NonfreeKernelModules: nvidia_uvm nvidia
ApportVersion: 2.20.1-0ubuntu2.18
Architecture: amd64
CurrentDesktop: XFCE
Date: Sat Mar 16 09:30:55 2019
EcryptfsInUse: Yes
InstallationDate: Installed on 2015-11-21 (1210 days ago)
InstallationMedia: Xubuntu 15.10 "Wily Werewolf" - Release amd64 (20151021)
SourcePackage: coreutils
UpgradeStatus: No upgrade log present (probably fresh install)