Joe Worsley laughs. "I've gone native," he tells BBC Sport.

When he talks tactics now, he occasionally struggles to recall the English jargon so used is he to their French equivalents.

Who better then to give the inside track on Racing 92 and Toulouse, who pair off with Saracens and Exeter respectively in this Saturday's Champions Cup semi-finals?

Racing rendez-vous for Saracens

Racing 92 have had some formidable former fly-halves. New Zealand points machine Dan Carter spent three years in Paris. Before him Ireland's Johnny Sexton and Argentina's Juan Martin Hernandez brought their distinctive, different styles to the shirt.

Now, it is the turn of Scotland's maverick playmaker Finn Russell. And he is doing it rather well.

"He doesn't look like much, but he does everything for them," trilled French sport newspaper L'Equipe earlier this month, describing Russell as the "most spectacular fly-half in the Top 14".

One of Worsley's first games on the touchlines at Castres was a 27-0 defeat by Racing back in January.

"Finn Russell was fantastic that day," he remembers. "He has been in prime form for the past couple of weeks.

"He has radically changed their threat in attack.

"Previously they had some exciting players who could break a tackle and make an offload on their own. Now they have someone who can bring all these players into the game much more.

"Wing Juan Imhoff is a very intelligent player, the way he reads Russell's intentions make him a big threat, while centre Virimi Vakatawa has really benefited from Russell putting him into holes.

"Russell's arrival has created an attack that can threaten out wide or near the ruck. If you mess up your numbers, lose a collision or leave a bit of space, he has the vision and options to punish it."

Russell's yawning miss-passes and deft chips into space have made for bumper highlight reels this season. But Racing have also learned to mix pragmatism with the pyrotechnics.

"They don't overplay," explains Worsley. "That is something they have improved. If it is not going well, they don't keep banging away, they will kick to space and let the other team mess up."

Worsley highlights number eight Antonie Claassen as one of the star performers in pack that mixes heavy-duty ball-carrying with a huge appetite for the breakdown donkey work.

He believes that Saracens may be able to play at a pace that is uncomfortable for the French side however, with Top 14 matches, especially as officials enforce new laws around the breakdown, generally slower than those in the Premiership.

"Racing wouldn't have played at the level that Saracens played against Leinster, they will have to get used to the intensity of having the ball in play for 35-40 minutes," he added.

"Saracens have lost a bit of physicality, with the likes of George Kruis and Will Skelton departing. So, while they still have a fantastic group of players, they are a little weaker.

"I am going to go for Racing to win. I think they are in a really good place at the moment with a rounded game and a fantastic group of players."

Toulouse to win?

The reigning French champions against the runaway Premiership leaders. It may be that the day's second Anglo-French semi-final is the true 'Le Crunch', club edition.

It certainly comes with two contrasting styles.

"Toulouse have players who have scored straight from nothing. The likes of Cheslin Kolbe and Antoine Dupont attack instinctively, reading the space so well," explains Worsley.

"Defensively that is nigh on impossible to prepare for.

"Exeter are a very different team, very structured. You know what is going to happen. You just have to try to somehow stop it."

For all the backline flair, Worsley believes the battle will be won up front as Exeter impose their close-quarters game on a jumbo-sized Toulouse pack that includes 20-stone prop Charlie Faumuina and 6ft 10in second row Rory Arnold.

At 37, New Zealander Jerome Kaino may have lost some of his power and pace that made him a key part of two World Cup winning sides, but he now makes his biggest impact culturally rather than physically.

"Kaino has come in and done a bit of what Jonny Wilkinson did for Toulon - giving them a level of professionalism and leadership that they didn't have before," said Worsley.

"He is an intelligent guy who has lived in incredible rugby environments and has lifted up the whole team."

Like Racing, Toulouse have achieved a better balance between playing sensible and chancing the sensational in recent seasons.

The development of fly-half Romain Ntamack, the 21-year-old son of Toulouse legend Emile, has helped.

"He is a real talent," said Worsley. "Initially I thought he made too many mistakes and his kicking wasn't good enough, but he has been getting a lot better.

"I worked with his dad for a couple of years at Bordeaux-Begles and they were always on the phone talking tactics."

Worsley believes it will be the French side that triumphs.

"I would side with the French again," he said. "But I am really interested to see if the English sides can play with the pace that might upset Racing and Toulouse."