create table test
(id_lskill int identity not null,
lskillName varchar(100),
constraint PK_id_lskill PRIMARY KEY(id_lskill))

create table level_1
(id_level1 int identity not null,
level1Name varchar(100),
lskillN int,
constraint PK_id_level1 PRIMARY KEY(id_level1),
constraint FK_lskillN FOREIGN KEY(lskillN) REFERENCES test(id_lskill))

create table level_2
(id_level2 int identity not null,
level2Name varchar(100),
lvl1 int,
constraint PK_id_level2 PRIMARY KEY(id_level2),
constraint FK_lvl1 FOREIGN KEY(lvl1) REFERENCES level_1(id_level1))

create table level_3
(id_level3 int identity not null,
level3Name varchar(100),
lvl2 int,
constraint PK_id_level3 PRIMARY KEY(id_level3),
constraint FK_lvl2 FOREIGN KEY(lvl2) REFERENCES level_2(id_level2))

insert into test
(lskillName)
values('Russian'),('English'),('Deutsch');

insert into level_1
(level1Name, lskillN)
values('Level_1-Russian_1', 1),
('Level_1-Russian_2', 1),
('Level_1-English_1', 2),('Level_1-English_2', 2),('Level_1-Deutsch_1', 3),('Level_1-Deutsch_2', 3);

insert into level_2
(level2Name,lvl1)
values('Level_2-Russian_1', 1),
('Level_2-Russian_2', 2),
('Level_2-English_1', 3),('Level_2-English_2', 4),('Level_2-Deutsch_1', 5),('Level_2-Deutsch_2', 6);

insert into level_3
(level3Name,lvl2)
values('Level_3-Russian_1', 1),
('Level_3-Russian_2', 2),
('Level_3-English_1', 3),('Level_3-English_2', 4),('Level_3-Deutsch_1', 5),('Level_3-Deutsch_2', 6);