The word for "chicken", is it [gai] or [kai] (tone omitted)? Does the g sound exist in Thai and Lao? The answer is maybe, but only in very limited environments, and it varies across native speakers.
First, /g/ and /k/ are both unaspirated velar stops, but the /g/ is voiced while the /k/ is voiceless. The /k/ in transcriptions often causes confusion with the aspirated /k/ in English, e.g. kill (aspirated) vs skill (unaspirated). In Thai and Lao, the aspirated and unaspirated /k/'s are separate phonemes, (aspirated k is usually transcribed as kh) whereas in English, there is only one /k/ phoneme. So you could have a minimal pair such as kaa 'crow' vs khaa 'stuck.'
However, there is no /g/ phoneme in Thai and Lao. If you were to substitute kaa 'crow' with [gaa], your pronunciation would slightly be off, though you would still be understood. People will just think you have an accent. Since there is no /g/ phoneme in Thai and Lao, native speakers cannot hear any difference between the /g/ and the unaspirated /k/.
Most English speakers find it hard to produce the unaspirated /k/--unless they also speak Spanish or other languages that have unaspirated /k/. Many feel that the unaspirated k is a [g]. This might be because in English when g occurs initially, e.g. get, it gets slightly devoiced, but when it occurs medially, e.g. forget, it is fully voiced.
Thus, if you want to improve your Thai or Lao accent, work on your unaspirated k! One of the many tricks is to say words like "skip" "scar" "scheme" repeatedly. Feel your k's. Then try to get rid of the s while still maintaining the k. So for "skip", for example, try to go from skip to -kip, and do not allow yourself to aspirate the k.