Each of the last three summers, the Celtics have turned to an underutilized talent pool abroad for rotational fortification. Two years ago, the team plucked Daniel Theis from Brose Bamberg in Germany. He’s played two seasons in Boston and just locked in two more. Last summer, it was Brad Wanamaker from Turkish powerhouse Fenerbahce. After a successful rookie season in green, Wanamaker is returning on a second deal for 2019-20.