Since FG commit f105e8dfb2f[1], child nodes of <localized> in
addon-metadata.xml must use a hyphen instead of an underscore as the separator
between language and territory (this is more in line with the usual naming
scheme for property nodes in FG).
[1] https://sourceforge.net/p/flightgear/flightgear/ci/f105e8dfb2fb481770bb85e498a99e15da13ca32
