A QUOTE by Pliny the Elder (AD 23-AD 79) accompanies Alterum, the fifth album by Julie Fowlis. Describing the land of a Scandinavian tribe, the Roman scholar said: “alterum orbem terrarum eam appellant”, that is: “they call it the other world”.

Otherness and mystery are the first impressions this graceful record gives; the Edwardian-style white dress and feathery head gear Fowlis wears on its cover recalls that era’s fascination with the supernatural while its opening track A Phinthrag’s a Phinthar (O Sister Beloved Sister) — a duet with Nashville songstress Mary Chapin Carpenter — tells of a girl’s entrapment by the fairies.

And though Fowlis has brought Scots Gaelic, the language of her native North Uist, to mainstream audiences for over a decade — most notably as the spring-clear singing voice of Merida in Disney-Pixar’s 2012 animation Brave — it’s only spoken by less than one per cent of the country’s population. It remains a language of “otherness”.

Gathering songs for this record, she says, she was struck by a common theme running through many.

“If I hear a song I’m interested in, in any language, I’ll note it down,” Fowlis says from her home near Inverness. “When it came to last autumn, the start of the winter, I went to the list and by chance, the first four or five songs had a connection to the other world, the Gaelic other world. These amazing tales, some of them quite old. I wondered: ‘Is this a sort of sign about the thread through the album?’”

Fowlis was reminded of a time early in her professional singing career when BBC DJ Mark Radcliffe had described her songs as being “like messages from another world”.

“I thought it was strange that he had chosen to use those words: ‘from another world’,” she says. “That struck me very deeply, that though I was singing in a language that had been spoken for a thousand years and more, people still consider it to be foreign. It was striking, and it resonated with me.”

Alterum sees Fowlis looking to other languages and cultures as well as embracing Gaelic folklore and the natural world in the likes of the melancholy Oran An Roin (Seal Song) and Cearcall Mun Ghealaich (Circle About The Moon), the album’s celestial closing track which is based on verse by Skye poet Catriona Montgomery.

Singing in English for the first time on one of her own albums, there’s a rendering of Archie Fisher’s Windward Award — another duet with Chapin Carpenter — and a gorgeous take on Go Your Own Way, learned from Annie Briggs. Elsewhere there’s the dignified, poignant Camarinas, a traditional Galacian song translated into Gaelic by Fowlis’s South Uist singing partner Gillebride MacMillan — known to viewers of Outlander as Gwyllyn The Bard.

The idea of “other worlds” was taking on social and political aspects too, she explains.

“Thinking about the Gaelic other world got me thinking about the other worlds that we all inhabit everyday,” says Fowlis, who is married to multi-instrumentalist and composer Eamon Doorley. “We speak three languages in our family: English, Scots Gaelic and Irish Gaelic. We exist between different language worlds, and with that we jump between different social worlds and different communities and different people.

‘‘Over the last few years we’ve seen these massive political changes, in Scotland, the UK and in Europe. It’s unsettling too, and makes you think about the world that we live in, and how the borders are moving and shifting.”

Including Go Your Way and Windward Away was, Fowlis says, part of her intention to “reach out to other traditions that I’ve learnt so much from.” It’s evident she’s genuinely touched to have been given Briggs’s blessing to cover the track written around 1971.

“It was a great privilege to be given the thumbs up by her,” says Fowlis. “Like Annie, an English folk singer with links to both Ireland and Scotland, I wanted to acknowledge Archie Fisher with Windward Away and all he’s done for the Scottish tradition.”

At least two aspects made Alterum different from previous albums Fowlis and Doorley have worked on. Though the pair produced the album themselves, veteran engineer Calum Malcolm was, Fowlis says, “totally in charge of how it sounded”.

“He made sure the sound was consistent and to a very high standard,” she says. “We would spend an incredible amount of time geeking out over a microphone, just to make sure we had the right acoustic sound on everything that we wanted. Calum worked really hard on that, on keeping the sound very true to the instruments, so that when you hear an instrument back through proper speakers it almost feels like the instrumentalist can be playing in the room. As an acoustic musician, that’s what you’re always striving for, that live sound. We wanted to grasp that movement and energy that we have, the pushing and pulling in the song that happens naturally when you’re performing.”

Playing at these gigs with Fowlis and Doorley will be guitarist Tony Byrne, with whom the pair worked closely with for Alterum, and fiddler Duncan Chisholm. The extended line-up will change from concert-to-concert, Fowlis says, with likely guests along the way including contributors to the album such as double bassist Ewen Vernal, cellist Su-a Lee, violinist Greg Lawson and Donald Shaw. The latter, the artistic director of Celtic Connections and a founder member of trad supergroup Capercaillie, wrote string arrangements for three of the tracks — the second difference for the pair.

“It’s by far and away the most enjoyable record we’ve ever made and the one that we’re most happy with,” says Fowlis. “Maybe it’s partly to do with being a bit older, being sure of how I wanted it to sound, and of what I wanted to say.”

That sense of self-belief struck Fowlis as they headed to the Fife studio of Malcolm — an acclaimed engineer/producer for over 40 years — to use his vintage equipment. “We were talking about using the old sounds, the old microphones in Calum’s studio, and I thought that this is what we were doing with the songs too, going back to older songs,” she says. “There’s merit in that: things don’t always have to be new.”

There are only 60,000 speakers of Scots Gaelic. When a language is lost, so is a particular culture, a particular world.

“There is so much to learn from these stories,” Fowlis says. “There is so much there, from local history and place names, to a much deeper history of folklore and belief systems. All of these kind of pointers and hints are in the songs. Some might want to write them off as fantastical tales but they are much, much more than that.”

Nov 24: Celtic Sessions double bill with Session A9, Perth Concert Hall, 7.30pm. www.horsecross.co.uk

Jan 20: Celtic Connections, City Hall, Glasgow, 8pm. Tel: 0141 353 8000

Jan 26: Celtic Connections: Songs of the Gael with Karen Matheson, Kathleen MacInnes and others, Royal Concert Hall, Glasgow, 7.30pm. Tel: 0141 353 8000

Jan 28: Eden Court Theatre, Inverness, 7.30pm Tel: 01463 234 234. www.eden-court.co.uk

Feb 2 and Feb 4: Celtic Connections: Transatlantic Sessions, Royal Concert Hall, Glasgow, 7.30pm, Tel: 0141 353 8000. www.celticconnections.com