One good man wrote an article for me how to translate WDA applications in SAP. Sergey, thank you!

There are three ways to do translation:

1. Online Text Repository (OTR) (transaction SOTR_EDIT)
2. Configuration translation in SE63
3. Data element translation

To find out where to find needed element for translation we need to open WDA component configuration:
trans_1


trans_2

trans_3

In configuration we can see names referencing to Online Text Repository (OTR).
Open transaction SOTR_EDIT:

trans_4

trans_5

trans_6

On the left side there are all links used in configuration. Here we do translation. THe same way we can view and change text for any specific text in configuration:

trans_7

SOTR_EDIT:

trans_8

trans_9

Some fields have no reference to OTR.

trans_10

In this case we use SE63 transaction. In this regard we need to find full configuration name. We need component name used for configuration:

trans_11

SE80:
trans_12

Look for our configuration:

trans_13

Then SE63:
trans_14

trans_15

Third way is to use data element translation for screen structure. I used this to translate screen elements.

Here we can find screen structure used for infotype:

trans_16

Or here:
trans_17

trans_18

trans_19

trans_20

trans_21

Here you do translation for data elements that is referenced by screen field. Translation will be shown during user logon.