This file defines intelligence influence on characters abilities like success in spell learning or max possible maximal spells level that can be obtained by creature.
The first row (titles of columns ) is filled by the names of features affecting of PC (like LEARN_SPELL).
The first column is filled by value of intelligence of character.
The rest columns are filled by values for given intelligence - pretty obvious from names I suppose.
In BG TotS we have:

 2DA V1.0
 0
           LEARN_SPELL MAX_SPELL_LEVEL MAX_SPELLS_PER_LEVEL
0          0           0               0
1          0           0               0
2          0           0               0
3          0           0               0
4          0           0               0
5          0           0               0
6          0           0               0
7          0           0               0
8          0           0               0
9          35          4               6
10         40          5               7
11         45          5               7
12         50          6               7
13         55          6               9
14         60          7               9
15         65          7               11
16         70          8               11
17         75          8               14
18         85          9               18
19         95          9               99
20         96          9               99
21         97          9               99
22         98          9               99
23         99          9               99
24         100         9               99
25         100         9               99