Usage of language tags in SKOS

Hi all,

looking at
http://www.w3.org/TR/2009/WD-skos-primer-20090615/#secnotations
I am wondering if SKOS recommends the usage of language tags in an
appropriate manner. I am not sure about this passage:

[
However, the management of such datatypes can be cumbersome. Further, the
previous pattern is not really needed when publishers consider the notations
themselves to be simple language-independent labels. In such cases, it is
possible to use one SKOS labeling property, for instance skos:prefLabel, in
combination with private use language tags (or subtags) as defined by RFC
4646 [RFC4646]. This pattern was first proposed for a list of coded
countries [COUNTRYCODES-SKOS] from which the following example is adapted:
iso3166:FR skos:prefLabel "France"@en ;
  skos:prefLabel "FRA"@en-x-notation-threeletter ;
  skos:prefLabel "250"@x-notation-numerical.
]

First, private use language tags are recommended to be used for a
"language-independent-label", which seems to be a contradiction in itself.
Second, the labels are used for specifying the language of notations as part
of e.g. classifications. Notations for classifications are not natural
language, but rather closer to identifiers in programming languages, so it
seems to me that usage of language tags is not appropriate for this purpose.
Any comments?

Best,

Felix