If France and Italy corrected their labour costs, how long would it take for this strategy to be successful?

Germany in the early 2000s and Spain from 2009 conducted internal devaluations (a reduction in labour costs to improve companies’ cost competitiveness and profitability). In both cases, this policy proved to be effective in restoring exports, investment and employment after a few years. France and Italy currently have a problem of cost competitiveness (given their level of product sophistication) and profitability, but reject the idea of an internal devaluation. If France and Italy decided to finally conduct an internal devaluation, how long would it take for this strategy to be successful ? Initially, it drives down per capita GDP and t hen it boosts it; how long would it take for per capita GDP to rise above the level it would have reached without internal devaluation? The examples of Germany and Spain show that this timeframe is four to eight years, which is obviously very long and discouraging.