I think you might be misapprehending the nature and structure of the 'Forest Brothers'. The Lithuanian, Latvian, and Estonian insurgent groups which generally fall under the 'forest brother' descriptor were all nationalist movements (as was the major Ukrainian resistance movement, OUN/UPA). They were concerned primarily with attaining sovereignty in the long run for their respective national entities, although anti-Bolshevism and anti-Semitism were sometimes part and parcel. The partisan groups varied in terms of their centralization and unity, and generally did not coordinate cross-national operations as far as I am aware. The most centralized of the anti-Soviet insurgencies was the Ukrainian Insurgent Army (UPA), while the Baltic groups were much less so. There were three major insurgent groups in Lithuania, as well as a number of other small bands. They attempted to unify under the Lithuanian Freedom Fight Movement in 1949, but in practice the LFFM's leaders could never develop a coherent strategy. Alexander Statiev's description of the Lithuanian partisan movement speaks somewhat for the Estonian and Latvian movements as well: "Most guerrilla units followed general guidelines sent from above, but their policies varied with their commanders, and they fought independent wars against the Soviets." (Statiev, The Soviet Counterinsurgency in the Western Borderlands, 114) Indeed, the leadership of the Latvian and Estonian insurgents were entirely wiped out by 1946 and 1949 respectively, and the guerrillas were reduced to fighting as small dispersed bands in the woods. These small bands did not coordinate cross-national actions - they were too small and their aims too modest to attempt pan-Baltic resistance efforts, at least not as far as I have encountered in my readings. Any trans-national interactions would have to be mediated either with a translator, or with the usual awkwardness of two people who only understand a few simple words in each others' tongue: Latvian and Lithuanian are far more distinct than, say, Spanish and Portuguese, and Estonian is different altogether. The Soviets did introduce Russian language instruction in schools when the occupation began, but not all of the fighters would have had any schooling during this time, and the idea of anti-Soviet, ostensibly anti-Russian nationalists communicating in Russian as a sort of lingua franca strikes me as unlikely.