Being certified will certainly make you more marketable and, perhaps more importantly, it will prepare you for the job. However your level of proficiency in English, and the fact that you don’t have a degree will represent a problem when applying for work outside your own country.
As for whether to opt for an onsite or online course, that really depends on how much time, money, and commitment you are prepared to invest. Online courses offer a great training opportunity at entry level. They can provide a thorough grounding in a new career and the right tools to approach a new profession within a manageable amount of time and finances.