I've always thought of the langseax as a typically early Anglo-Saxon weapon, peculiar to their lands. Are there any examples of langseaxes found outside of direct Anglo-Saxon influence? For example in Francia or Scandinavia? If so do the styles mirror their smaller regional counterparts or are they broken-back as with the English examples?

I've been thinking about the single edged Norwegian Viking Swords, which are thought to have evolved from the seax not the spatha. To me this seems like a big leap from a small knife to a full-sized sword? Maybe we're missing a link.

The langseax is pupular on the continent. It is not the broken back type, but rather has a centered spear point profile.

There are also big weapon knives in scandinavia (at least in Sweden: those are the finds I´ve been looking at) that follow a slightly different route of development apart from continental Europe and Britain.

Early viking age or slightly before, there are hugh single edged blades with a blade length of some 70-90 cm, that are wider towards the point and an upswept point: a gigantic puukko, but with a two handed (or even "three handed") grip. I have personally seen some half dozen of these monster blades in museum store rooms around Sweden. Not common in the find material, but they do exist.
Earlier on, during Vendel period, there are also big seaxes (55-65 cm blade), but not the broken back type. More continental in outline, even if the point droops some (I think these are labeled "atypical bretisaxe" typology wise). The curve of the back is "softer" and the edge is almost straight: often lifting a little towards the point, sometimes having a slight concave curve in the middle of the blade.

The anglo-saxon patterned broken back seax, you do not find much in scandinavia (in Sweden, at least. I am not certain about situation in Norway and Denmark). You do find influences of continental European seaxes in the great big late single edged blades.
The famous narrow and straight military knife (blade length about 45 cm) found in Birka and other places (by some called a seax: I am not sure about that. I rather call them war knives) seem to have eastern influences to its design even if they were made locally in eastern scandinavia and western baltic region. In Uppland and Gotland these long & narrow knives were popular among the elite, but you find them in graves distributed over a wider area.

There is a transition from a long straight backed single edged blade with organic hilt to the classic single edged sword so typical for Norway. The transition from organic hilted seax to fully hilted sword, seems to have taken place by the beginning of the viking age. This development seems to have been mostly taken place in Norway.

Long seaxes are far from uncommon in France/continental Europe. I personally had the chance to get close to several of them, in the 70-90 cms range. Most of them the curved back type, often with pattern-welding. Huge beasts, thick and yet fast, sharp and pointy, made for maiming.

Looks like we also had big single-edged hilted and pommeled things in the 10th century (almost), though it may have beeen something brought in by them northerners.

There is an important and forgotten one of langbardian origin, decorated with runes quite like its famous cousn from Beagnoth at the British Museum, lying somewhere in the warehouses of the Marzoli collection.

It was briefly exposed a couple years ago and then sent back to dusting.

Studied by Peter Johnson, though.

We have a 90cm-one in Bavaria, near where i have my workshop. I guess it was pattern-wielded, with a long hilt. Migration-type.

A few examples :

This one is 728 mm, found in the Saône river (in Ouroux) :
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This one is 788 mm, found in the Doubs river in Pontoux :
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The one on the right is 730 mm, but the tang is broken. Found in the Seine river (La Rochette) :
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Thanks for all the replies. Very informative.