Back in the days of NFL Europe, teams were allowed to keep nine guys on their practice squad if one of the spots went to an international player. That exemption hasn't been utilized in years considering NFL Europe shut down back in 2007, but the rule technically still exists.
It turns out that the Detroit Lions actually tried to make use of the rule this year with kicker Havard Rugland, who was released by the team in August. As discovered by SideLion Report, a story from Norway mentioned that the Lions applied to get Rugland on their practice squad as an international player, but the NFL apparently shut them down. Why? Based on the translation of the article, it's suggested that the rule "was made in terms of NFL Europe." Even though it still exists, the NFL apparently doesn't believe it should be utilized in Rugland's case.
So why didn't the Lions simply add Rugland to the practice squad as one of the eight regular players? I'm assuming they didn't want to take up one of their usual spots with a kicker. That's understandable, because those eight spots were spent to add extra depth at certain positions. At kicker, extra depth doesn't really come into play. If there's an injury or a change needs to be made, you simply go out and sign another kicker. It just wouldn't make much sense to use a practice squad spot on one.
In the case of Rugland, the Lions saw an opportunity to keep a kicker around as the ninth member of their practice squad. It was a smart move on their part to try to utilize that rule, but the NFL apparently saw things differently. As a result, Rugland is a free agent, and he's currently back in Norway waiting for another chance to join an NFL team.