These words are predominantly used in Argentina.
Bárbaro means good. If something is "bárbaro" it means that it is "More than fine".
- adj. Excelente, llamativo, magnífico. El orador estuvo bárbaro. (from RAE)
Josha requires a bit more explaining. The word was spelt josha but it was referring to the term joya. Joya means “great”, “excellent”. For example, this website describes joya as “awesome”, “right on”, and lists the expression as an essential in the Argentinian jargon. The word joya is also used to describe someone’s mood, eg: Estoy joya (“I am joya”), which means “I am happy” (compare with “I’m A-okay” or “I’m peachy”).
As for why the author wrote josha instead of joya, the term joya is predominantly used in Argentina. Argentinians tend to pronounce the Spanish "y” as a "sh" or “zh” (sheísmo), so the person used the literal pronunciation, which is usually done as a joke. Other examples of this phenomenon are:
Tweet: “Estoy shorando de la emoción 😭” (Source]
YouTube title: “Tah shoviendo con sol xD” (Source]
As you can see, this form of phonetic transcription is only done in very colloquial contexts. For more on Argentinian phonology, see Rioplatense Spanish.