The nationalists of the various Spanish regions are indeed left wing, as are the Celtic nationalists. Nationalism was unleashed by the French Revolution and was left wing long before it was right wing. Today most left wingers are nationalists of one sort or another.
Unfortunately, the vast majority of nationalists of other peoples, left or right, are anti-Jewish and anti-Israel. Somehow they have located in Zionism the "real power" behind globalism, internationalism, and modernity. For this reason non-Jewish nationalists, even the most right wing, sound just like Communists when they talk about Israel ("oppression," "liberation," etc.). Nationalists all support each other, seeing in other nationalisms sister movements to their own, but the oldest nationalism in the world, and the only BIBLICAL nationalism, is not only an enemy, but The Ultimate Enemy. Why is this?
I believe the answer lies in the "palaeoconservative" doctrine of "ethnopluralism," aka "a planet of peoples." According to this worldview, each nation should have its own particular "truth," have its own "gxd," and live in its own "holy land." Xianity, despite its universalist pretensions, is radically local- and national-oriented, so it is easily co-opted by these anti-Jewish nationalists.
As CHaZa"L said, the great sin'ah comes from Sin'ai. The election of Israel is an objective fact of history, and thus stands as a rebuke and a disproof of all the pretensions of the nations of the earth. Small wonder that instead of hailing Zionism as a sister movement they hate and despise it, often seeming to regard the very presence of any Jew (even one) as a sort of "black hole" which draws all non-Jewish "national integrity" into the abyss.
And while I used to be flummoxed by palaeo-right identification of Communism with the Jews, I believe I can see one reason for it now. Like the allegedly "science" based Communism, Judaism represents something objective and universal, something that corrodes subjective national mythologies in favor of Objective Universal Truth. This is the only thing Judaism ever had in common with Communism, and the identification of the two tells us a great deal about the mentality of the people who believe this way.
As for the historically undeniable proclivity of non-religious Jews to drift into left wing movements and causes, I believe (and yes, this is just a personal theory) that this is because Jews don't have the local roots that other peoples do--roots based in false local "gxds" and mythologies. The Jewish People are not numbered among the nations of the earth and their roots are quite literally in Heaven. When (G-d forbid!) Jews lose faith in HaShem, they have no localized heathen traditions to anchor them and quite naturally and understandably drift into universalistic movements. And what could be more universalistic than "science?" Perhaps this is all related to the fact that 'ein leYisra'el mazzal, which can also be read 'ayin leYisra'el mazzal--while all the nations have their own mazzalot Israel has none, or "Israel's mazzal is nothingness."
At any rate, alliances with secular non-Jewish ideologies is always going to be a mistake. If Zionists want to make their case to non-Jews then let them make the case for HaShem and the Torah, which is the true coin of which all the non-Jewish mythologies is the counterfeit. This alone will answer the emptiness of non-Jewish life and will ensure the safety of Jews among non-Jews far more than the three hundred year old habit of allying with the European "enlightenment."
Just one person's thoughts.