> My point of reference is the success of Polish domestic "Allegro" ecommerce platform, which was able to out-fox EBay, and later on Amazon, and still maintains dominant position on the local market.
Were eBay and Amazon unable to translate their websites into Polish quickly enough for some reason? I just checked https://ebay.pl and http://www.amazon.pl , the latter of which redirects to amazon.de with language set to pl_PL, but nonetheless appears fully translated into Polish.
> There were no significant technological advantages, nor any notable political connections. The platform won purely on being local.
To be clear, I'm not saying that being local doesn't matter. What I'm saying is that localization (in the sense of translating and adapting the website to local preferences) is the least hurdle in becoming local. The much bigger hurdle is acquiring local customers who are already used to local services. Either you have an obviously superior product that local competitors can't match (unlikely for run-of-the-mill online stores) or you're fighting an uphill battle.
> In spite all the local success the platform could not expand to the west of Poland due to localization (language and partly culture). It did expand a little bit to Ukraine and Czech Republic.
My guess is that there are Czechs and Ukrainians in Poland who got familiar with Allegro there and spread it via word of mouth. (I could not find a Czech or Ukrainian version of allegro.pl, so are they using the Polish site?) On the other hand there are likely many more Poles in Germany than Germans in Poland, so Poles would be more familiar with German services than Germans with Polish services. (Case in point: the redirect from amazon.pl to .de)