A year after Amazon opened in-skill purchasing to all Alexa developers in the U.S., the company is launching the service internationally. Initially, the capability will roll out to developers in the U.K., Germany and Japan, and then developers elsewhere in the world. With in-skill purchasing, developers are able to generate revenue from voice apps in a number of ways: through the sale of digital goods as a one-time purchase, subscriptions or consumables.

Digital goods can include things like expansion packs for a trivia skill, while consumables are one-time-use purchases — like hints for a trivia game. Subscriptions, meanwhile, give developers a more consistent revenue stream, and can be used for things like a premium, upgraded app experience or a voice app that regularly updates with new content, for example.

The larger idea is that publishers need to make money from voice apps in order to make their continued development worth their while. As it’s still early days for voice; many developers are still seeing what sort of skills work and which don’t, and how customer loyalty plays out over the long-term.

There are now more than 80,000 skills for Alexa, which means there’s a long tail of developers whose apps aren’t getting much traction and only a few hits.

But Amazon today highlighted a couple of skills finding some success. One is the game skill Escape the Airplane from developer Gal Shenar, who reports a 34% conversion rate. Nick Schwab’s ambient sound skills, meanwhile, have attracted nearly 2 million monthly active users. He offers those customers free trials and monthly subscriptions, and 30% convert to trials. A further 90% of the free trials then convert to paid subscriptions.

In both cases, the developers present the premium experience as an option — not a hard sell. And they make their skills engaging and habit-forming.

Other top skills include Jeopardy!, Escape the Room, Beat the Intro, Big Sky, Would You Rather for Family, Question of the Day and Yes Sire.

With the international expansion, developers will be able to monetize their skills with localized content that’s relevant to customers in different countries. They can do so using either the Alexa Command-Line Interface or the Alexa Developer Console.

Interested developers are asked to sign up by way of a form to connect with a member of the Alexa team about their idea.