In an interview with Asus CEO, Jerry Shen in September 2017, he confirmed that the ZenFone 5 smartphone series will be introduced to the market as early as March 2018. It looks like he is keeping to that promise as the ZenFone 5 Lite has been recently certified in Russia.
The model number for the phone is ZC600KL, which indicates that it will be running on a Snapdragon chipset with support for LTE connectivity, and the number 60 in the model number indicates that it will come with a 6-inch screen. Wheather it will be an 18:9 screen ratio is still unknown. There is also no indication on the release date or if Asus will be unveiling the ZenFone 5 series at MWC 2018 next month.
We will know more about the phones when it comes closer to the release date, but we can say for sure that we should be seeing the phones before Computex, as they released the ZenFone 4 series during the 2017 Computex event.