The Lost Tribe of Issachar is modern Serbia and all affiliated countries.
The Congress of Berlin met in 1878 to reorganize the countries of the Balkans following the Russio-Turkish war.
As part of that process Serbia was recognized as an independent nation.
The timing, which follows Issachar's Seal Date, identifies the Balkans as the location of Issachar and the general collection of nations in that area as the nations that make up the Lost Tribe of Issachar.
For most of the 1900s, this was known as Yugoslavia, or South Slavia.
Nations that make up this tribe are characterized by their sharing what is called a South Slavic Language.
Jacob pronounces a blessing over Issachar that describes his eventual location in the world.
1 Genesis 49:14-15 14יִשָּׂשכָ֖ר חֲמֹ֣ר גָּ֑רֶם רֹבֵ֖ץ בֵּ֥ין הַֽמִּשְׁפְּתָֽיִם׃ 15וַיַּ֤רְא מְנֻחָה֙ כִּ֣י ט֔וֹב וְאֶת־ הָאָ֖רֶץ כִּ֣י נָעֵ֑מָה וַיֵּ֤ט שִׁכְמוֹ֙ לִסְבֹּ֔ל וַיְהִ֖י לְמַס־ עֹבֵֽד׃ (WLC)
1 Genesis 49:14
1 Genesis 49:14-15 14Issachar is a strong ass couching down between two burdens: 15And he saw that rest was good, and the land that it was pleasant; and bowed his shoulder to bear, and became a servant unto tribute.(KJV)
1 Genesis 49:14-15 14Issachar is a strong ass couching down between 2 burdens: 15And he saw that rest was good, and the land that it was pleasant; and bowed his shoulder to bear, and became a servant unto tribute.(KJV/NC)
1 Genesis 49:14-15 14Issachar is a strong ass,
Couching down between the sheepfolds:
15And he saw a resting-place that it was good,(ASV)
1 Genesis 49:14-15 14Issachar is a mighty man couching by the highways; 15And he saw that his dwelling place was good, and his land fertile; and he bowed his shoulder to servitude, and became a servant to tribute. (LAM)
1 Genesis 49:14-15 14Is'sachar is a strong ass, crouching between the sheepfolds; 15he saw that a resting place was good, and that the land was pleasant; so he bowed his shoulder to bear, and became a slave at forced labor. (RSV)
1 Genesis 49:14-15 14"Issachar is a rawboned donkey lying down between two saddlebags. 15When he sees how good is his resting place and how pleasant is his land, he will bend his shoulder to the burden and submit to forced labor. (NIV)
1 Genesis 49:14-15
14'Issachar is a strong donkey,
Lying down between the saddlebags.
15He saw a resting-place, that it was good,
The land, that it was pleasant;(WEB)
1 Genesis 49:14-15
14'Issachar is a strong donkey,
lying down between the saddlebags.
15He saw a resting place, that it was good,
the land, that it was pleasant.(WEB/HNV)
1 Genesis 49:14-15 14Issachar is a mighty man crouching by the highways; 15And he saw that his dwelling place was good, and his land fertile; and he bowed his shoulder to servitude, and became a servant to tribute. (BRB)
Yugoslavia sits on the land trade-routes between Europe and Turkey, and from there to the east, India and China, and by land to Africa as well. This location on the trade routes, is hinted at in the prophecy over Issachar.
The other idea that Jacob hints at with Issachar is that he would submit to forced labor.
The Seal Date event was a peasant revolt in the Balkans that broke off Ottoman rule over the South Slavic peoples. This is the bondage that Jacob is hinting at. They would also come under Communist rule in the early 1900s, and then later NATO rule (and bombing)...
The main characteristic of Issachar is his inability to stand alone as an independent people.
The dark green in the following map shows the peoples who share South Slavic languages and form the basis for Issachar.