In the default game, the subtropical climate only gets access to steam, diesel, monorail, and maglev locomotives (only the temperate climate gets access to electric). In order to get electric locomotives, you need to install a mod (known as a "NewGRF").
In the desktop version, the easy way to install NewGRFs is to click "Check online content" from the startup screen, pick a suitable NewGRF ("2cc TrainsInNML" is probably the most popular, providing over a hundred real-world locomotives), double-click the name or click the tiny little checkbox to the left of the name to select it for downloading, and click "download". Once downloading is finished, click "Close" to exit the online-content dialog, and select "NewGRF Settings" from the startup screen. Find the NewGRF you just downloaded in the "Inactive NewGRF Files" list, click "Add", and then click "Apply Changes". Close out of this dialog and start a new game.
If you're using the 2cc trains, you'll probably want to restrict which trains are available -- the full set is rather overwhelming. To do this, click the "NewGRF Settings" button, highlight the "2cc Trains In NML" entry in the "Active NewGRF files" list, and click "Set parameters". Scroll down and select the regions that you want to use trains from.
I don't know if this applies to the Android version, but I assume it does -- modding is a major part of OpenTTD.