I can't think of an easy way to do this entirely in Word, but if you also have Excel:

Open a blank Excel worksheet.
Starting in cell A2, type an A, then enter. Type a B in A3, another A in A4, and another B in A5. Then select those ABAB cells and grab the fill handle and fill down to a couple of thousand rows. You'll want those for filtering.

Then, copy your text in Word and paste into the Excel sheet starting in cell B2. While it's still copied to your clipboard, ALSO paste it a second time starting in cell C3. You should now have the Spanish entry and the English entry side-by-side.

Select the whole area including your A "helper" column with the A's and B's, and activate a filter (Data/Filter). Select "B" in the A column, and those should have the rows that start with the English word and have the next Spanish word next to them. Delete these rows, and clear the filter.

Copy the Excel contents (without the A column, as you don't need those "A"s any longer, and paste into Word. It should automatically paste as a table; you can then go to the Layout section of the ribbon and Convert table to text, using a tab as the "separate with" between columns.

I'm sure there's a simpler way, but that works.