Which is the optimal climate to raise walnuts?
Walnuts can be grown under those conditions. They are grown in most areas of the United States except for the very cold areas of the northern plains. I would choose cold hardy varieties as the non-old hardy varieties are damaged by temperatures of -5 C. You need at least 2 varieties for cross pollination and most commercial farms have several. They have separate male and female flowers on the same tree which do not bloom at the same time to prevent self pollination, so choosing pollinizer varieties can be tricky. It does take a long time for the trees to come into bearing so return on investment is long term. A more appropriate area for information applicable to Albania might be Turkey, another Balkan country or Hungary.