The fluff may vary but it is a constant in the WarHammer universe that Elves of any kind (Wood, High or Dark Elves) are xenophobic and look down on other races. Defiance towards other races is actually a common feature of most races in the Old World, but the Elves put the concept of isolationism to a new height.
From the WarHammer wikia,
The Wood Elves, (...) are a reclusive, secretive and highly isolationist race of Elves that have long ago voluntarily split off from the rest of their kin, preferring instead to live out their lives in Nature's embrace beneath the enchanted forested canopy of Athel Loren.
If possible, the Wood Elves are more reclusive than the High ones. They decide to live in harmony with Nature within boundaries of Athel Loren. I believe that they would interact with strangers only to protect their domain and deal with intruders. They will wander outside Athel Loren only when extreme circumstances need it:
they do not seek to act as the world’s protectors, (...) there are those times when the will of Orion and Ariel (...) must shape the fortunes of those that live beyond the boundary of their homelands.
Concerning Bretonnia: the only natural allies of Wood Elves would be their cousins from Ulthuan. Due to proximity and/or common enemies, humans, dwarves and lizardmen are occasional allies of the Wood Elves.
Amongst these occasional allies, the Bretonians are the closer ones. Their alliance started from the war between Wood Elves and Beastmen (their natural enemy, as embodiment of the corruption of nature) known as the Secret War:
The Secret War began in IC -815 when Cyanathair (also known as Morghur, Lord of Skulls) invaded Athel Loren. It is known as the Secret War generally because it only occurred between the Wood Elves and Beastmen, with other races and nations seemingly unaware that it has been raging for thousands of years.
During one of his attempts to destroy Athel Loren, Morghur tried to attack the Silverspire, a sacred ground for Bretonians. The Wood Elves then allied to the humans against their common ennemy and this result in another defeat of the Beastmen. After the battle, the humans seek to transform this alliance of circumstances into a durable, solid relationship. From WarHammer wikia:
When the Beastmen were defeated, the Wood Elves shrouded themselves in mist and slipped away, despite the humans’ attempts to treat with them. The Elves thought nothing more of their brief alliance — such things had happened before, and would doubtless happen again. (...) Many years later, that champion’s son braved the perils of Athel Loren in the hope of forging a lasting accord. (...)
As often with the Wood Elves, an alliance could be forged due to the good nature of Ariel:
The Mage Queen knew that whilst the spirit of the Silverspire endured, it would distract Morghur from feasting upon Athel Loren, and how better to ensure the spirit endured than to ensure that its human protectors thrived? Thus began a tumultuous friendship between the ancient realm of Athel Loren and the nascent kingdom of Bretonnia.
But this is a fragile alliance:
Common cause had brought friendship, but it was only good sense that the humans should fear their superiors. (...) There would never be lasting friendship between the two, but neither would there be enmity;
