Let me introduce 'The Big Issue,' a street paper from the UK that has launched in Japan, which can only be sold by homeless people.
Literal
Japan launch achieved UK origin [possessive-の] homeless people only [subject-が] sellers become-able street-paper 'Big Issue' [about-について] introduce [volitional-しよう].
A dense introductory sentence for a magazine profile. 日本創刊を果たした ('achieved its Japan launch') uses 果たす ('to accomplish'). ホームレスの人だけが販売者となれる ('only homeless people can become sellers') describes the business model. ストリートペーパー is the loan 'street paper.' 紹介しよう is the volitional ('let me introduce'). The sentence packs a lot of information into one long noun-modifying chain.