In 1917 King George V codified the styles and titles of prince/ss in Britain
He referred to it in Letters Patent as the 'style, title or attribute' of Royal Highness and the 'titular dignity' of Prince or Princess.
I'm wondering do other royal families use similar language or is it a matter for the government to decide the wording of titles.
I am not sure if I understood your question.
Anyway, in Belgium and in Spain, royal titles and styles are regulated by royal decrees, but, since the constitution says that all royal decrees must be countersigned by one or more responsible ministers, they are effectively regulated by the government.
In the Netherlands, on the other hand, royal titles and styles are regulated by an act of parliament, which was introduced in the Lower House by the ministers on behalf of the King (like most public laws BTW). The act of parliament in question, however, grants the King a discretionary power to confer some royal titles (like
Prins der Nederlanden or
Prins van Oranje-Nassau) on certain categories of people (e.g. the wife of the Prince of Orange, or the monarch's children other than the heir to the throne). As in Belgium and in Spain though, royal decrees must be countersigned by ministers, so, again, it is up to the government to decide who gets a titlle within the constraints set out in the law.
In any case though, Belgian, Spanish or Dutch titles such as e.g. as "
Prince/Princesse de Belgique", "
Duc/Duchesse de Brabant", "
Príncipe/Princesa de Asturias", "
Infante/Infanta de España", "
Prins/Prinses der Nederlanden". "Prins/Prinses van Oranje" etc, are not arbitrary, but rather defined in appropriate legal instruments with those exact names.
The Scandinavian countries , compared to the former aformentioned countries, seem to be a little bit more chaotic. Apparently, any person in the line of succession (currently only descendants of King Carl XVI Gustaf who are not disqualified by law) can be a prince or princess of Sweden, but the actual title the person gets seems to be a discretion of the Royal Court. For example, before 1980, when succession was still agnatic, all male descendants of King Karl XIV Johan had the title of
Sveriges Arvfurste (i.e. hereditary prince of Sweden), with the exception of the heir to the throne who was the
Sveriges Kronprins; a female descendant in male line of King Karl XIV Johan or the wife of a prince was, however, entitled a
Sveriges Prinsessa. After 1980, those titles changed: the heir is still called
Sveriges Kronprins (actually, now a
Kronprinsessa), but the new name for other men and women in the line of succession, as well as wives of princes and the husband of the Crown Princess, is simply
Prins av Sverige or
Prinsessa av Sverige. None of those titles are regulated by law (other than indirectly by the Act of Succession) or by an specifc executive order.
Furthermore, King Carl XVI Gustaf himself adopted a new simplified title ("
Sveriges Konung") in his declaration of accession to the throne (before him, his predecessors called themselves "
med Guds Nåde Sveriges, Götes och Vendes Konung"); apparently it is his choice to call himself whatever he wants to be called, unlike in Spain or Belgium for example where the title of the King is defined in law (in Spain, it is actually part of the constitution).
I am not sure about Denmark, but I believe that , as in Sweden, royal styles and titles are not regulated by law there either. The Danish court uses the title
Prins/Prinsesse til Danmark to refer to all people who are in the line of succession, and
Prins/Prinsesse af Danmark to refer to wives of princes in the line of succession and to members of collateral lines of the dynasty, who since 1953, have not been part of the line of succession (e.g. descendants in male line of King Christian IX who do not also descend from King Christian X and Queen Alexandrine). But, again , those titles seem to be arbitrary as is BTW Queen Margrethe II's own title of
Danmarks Dronning, which she also chose for herself (her father before her called himself, in a dispute of claims with the Swedes and other countries, "
af Guds Nåde Konge til Danmark, de Venders og Goters, Hertug til Slesvig, Holsten, Stormarn, Ditmarsken, Lauenborg og Oldenborg"
Furthermore, both in Denmark and in Sweden, when a prince or princess is excluded from the line of succession, e,g. because they married without consent, he or she also lose their royal titles and styles,although that seems to be also arbitrary. In Belgium, by contrast, as shown in the examples of Prince Alexandre and, more recently, for a brief period of time, Prince Amedeo, loss of succession rights seems to be dissociated from royal titles and styles. In the Netherlands, certain titles like "prince of the Netherlands" are lost though with loss of succession rights, but that is not arbitrary as in Denmark and Sweden, but rather mandated by law as the law ties those titles to membership of the Royal House, and membership of the Royal House, in turn, is tied to succession rights.
Well this may have been a way to avoid a family feud considering that Phillip is a cousin to both Michael and Constantine. 
